Preparation of 7-dehydrocholesterol and/or the biosynthetic intermediates and/or secondary products thereof in transgenic organisms

ABSTRACT

The present invention relates to a method for preparing 7-dehydrocholesterol and/or the biosynthetic intermediates and/or secondary products thereof by culturing organisms, in particular yeasts. Furthermore, the invention relates to the preparation of the nucleic acid constructs required for preparing the genetically modified organisms and to said genetically modified organisms, in particular yeasts, themselves.

The present invention relates to a method for preparing 7-dehydrocholesterol and/or the biosynthetic intermediates and/or secondary products thereof by culturing organisms, in particular yeasts. Furthermore, the invention relates to the preparation of the nucleic acid constructs required for preparing the genetically modified organisms and to said genetically modified organisms, in particular yeasts, themselves.

7-Dehydrocholesterol, also referred to as cholesta-5,7-dienol or provitamin D3, its biosynthetic intermediates of the sterol metabolism, such as, for example, zymosterol, farnesol, geraniol, squalene, lanosterol, cholesta-5,7,24-trienol and cholesta-5,7,22,24-tetraenol and its biosynthetic secondary products of the sterol metabolism, such as vitamin D₃ and cholesterol, are compounds of high economic value.

7-Dehydrocholesterol is economically important especially for obtaining vitamin D₃ from 7-dehydrocholesterol via UV irradiation.

Squalene is used as building block for the synthesis of terpenes. It is used in hydrogenated form as squalane in dermatology and cosmetics and also in various derivatives as an ingredient of skin and haircare products.

Furthermore, sterols such as zymosterol and lanosterol can be utilized economically, lanosterol being pivotal as crude and synthesis material for the chemical synthesis of saponins and steroid hormones. Due to its good skin penetration and spreading properties, lanosterol serves as emulsifier and active substance in skin creams.

An economic method for preparing 7-dehydrocholesterol and/or the biosynthetic intermediates and/or secondary products thereof is therefore of great importance. Particularly economic methods are biotechnological methods utilizing organisms which have been optimized by genetic modification and which produce 7-dehydrocholesterol and/or the biosynthetic intermediates and/or secondary products thereof.

While the sterol metabolism in bacteria, fungi, yeasts and some insects essentially goes from zymosterol via fecosterol, episterol, ergosta-5,7-dienol and ergosta-5,7,22,24-tetraen-3β-ol to ergosterol (provitamin D₂), the sterol metabolism in mammals essentially goes from zymosterol via cholesta-7,24-dienol, lathosterol to 7-dehydrocholesterol (provitamin D₃).

7-Dehydrocholesterol (provitamin D₃) is converted to cholesterol by 7-dehydrocholesterol reductase and cholesterol is converted to steroid hormones, corticoids and bile acids, such as progesterone, testosterone, estradiol, aldosterone, cortisone and cholate.

Some genes of the 7-dehydrocholesterol metabolism in mammals are known and have been cloned, such as, for example,

nucleic acids encoding a human Δ8-Δ7-isomerase (also referred to as emopamil-binding protein (EBP)), ACCESSION NM_(—)006579, and a murine Δ8-Δ7-isomerase (Braverman, N. et al., (1999): Mutations in the gene encoding 3β-hydroxysteroid-Δ8,Δ7-isomerase cause X-linked dominant Conradi-Hunermann syndrome. Nat. Genet. 22(3),291-294), nucleic acids encoding a human Δ5-desaturase (also referred to as sterol C5-desaturase), ACCESSION AB016247 and a murine Δ5-desaturase (Nishi, S. et al., (2000): cDNA cloning of the mammalian sterol C5-desaturase and the expression in yeast mutant. Biochim. Biophys. Acta 1490(1-2),106-108), nucleic acids encoding a human Δ24-reductase (also referred to as 24-dehydrocholesterol reductase (DHCR24)), ACCESSION NM_(—)014762 and a murine Δ24-reductase (Waterham, H. R. et al. (2001): Mutations in the 3β-hydroxysterol Δ24-reductase gene cause desmosterolosis, an autosomal recessive disorder of cholesterol biosynthesis. Am. J. Hum. Genet. 69(4),685-694) and nucleic acids encoding a human sterol acyltransferase (Chang, C. C. et al., Molecular cloning and functional expression of human acyl-coenzyme A:cholesterol acyltransferase cDNA in mutant Chinese hamster ovary cells, J. Biol. Chem. 1993, October 5; 268(28):20747-55) and a murine sterol acyltransferase (Uelmen, P. J.: Tissue-specific expression and cholesterol regulation of acylcoenzyme A:cholesterol acyltransferase (ACAT) in mice. Molecular cloning of mouse ACAT cDNA, chromosomal localization, and regulation of ACAT in vivo and in vitro, J. Biol. Chem. 1995 Nov. 3; 270(44):26192-201).

The genes of the ergosterol metabolism in yeast are essentially known and have been cloned, such as, for example,

nucleic acids encoding a Δ8-Δ7-isomerase (ERG2) (Ashman, W. H. et al. (1991): Cloning and disruption of the yeast C-8 sterol isomerase gene. Lipids. August; 26(8):628-32.), Nucleic acids encoding a Δ5-desaturase (ERG3) (Arthington, B. A. et al. (1991): Cloning, disruption and sequence of the gene encoding yeast C-5 sterol desaturase. Gene. June 15; 102(1):39-44.), nucleic acids encoding a Δ24-reductase (ERG 4) (Lai, M. H. et al., (1994): The identification of a gene family in the Saccharomyces cerevisiae ergosterol biosynthesis pathway. Gene. March 11; 140(1):41-9.), nucleic acids encoding an HMG-CoA reductase (HMG) (Bason M. E. et al, (1988) Structural and functional conservation between yeast and human 3-hydroxy-3-methylglutaryl coenzyme A reductases, the rate-limiting enzyme of sterol biosynthesis. Mol Cell Biol 8:3797-3808, nucleic acids encoding a truncated HMG-CoA reductase (t-HMG) (Polakowski T, Stahl U, Lang C. (1998) Overexpression of a cytosolic hydroxymethylglutaryl-CoA reductase leads to squalene accumulation in yeast. Appl Microbiol Biotechnol. January; 49(1):66-71, nucleic acids encoding a lanosterol C14-demethylase (ERG11) (Kalb V F, Loper J C, Dey C R, Woods C W, Sutter T R (1986) Isolation of a cytochrome P-450 structural gene from Saccharomyces cerevisiae. Gene 45(3):237-45, nucleic acids encoding a squalene synthetase (ERG9) (Jennings, S. M., (1991): Molecular cloning and characterization of the yeast gene for squalene synthetase. Proc Natl Acad Sci USA. July 15; 88(14):6038-42), nucleic acids encoding a sterol acyltransferase (SAT1) and (SAT2) (Yang, H.: Sterol esterification in yeast: a two-gene process. Science. 1996 May 31; 272(5266):1353-6.) and a further sterol acyltransferase (J. Biol. Chem. 1996, September 27; 271(39):24157-63), nucleic acids encoding a squalene epoxidase (ERG1) (Jandrositz, A., et al (1991) The gene encoding squalene epoxidase from Saccharomyces cerevisiae: cloning and characterization. Gene 107:155-160), nucleic acids encoding a C24-methyltransferase (ERG6) (Hardwick, K. G. et al.: SED6 is identical to ERG6, and encodes a putative methyltransferase required for ergosterol synthesis. Yeast. February; 10(2):265-9) and nucleic acids encoding a Δ22-desaturase (ERG5) (Skaggs, B. A. et al, Cloning and characterization of the Saccharomyces cerevisiae C-22 sterol desaturase gene, encoding a second cytochrome P-450 involved in ergosterol biosynthesis, Gene. 1996 Feb. 22; 169(1):105-9.).

Furthermore, methods are known whose aim is an increase in the content of specific intermediates and final products of the sterol metabolism in yeasts and fungi.

EP 486 290 discloses that the content of squalene and other specific sterols such as, for example, zymosterol, in yeasts can be increased by increasing the rate of expression of HMG-CoA reductase and simultaneously interrupting the metabolic pathway of zymosterol C24-methyltransferase (ERG6) and ergosta-5,7,24(28)-trienol 22-dehydrogenase (ERG5).

From T. Polakowski, Molekularbiologische Beeinflussung des Ergosterolstoffwechsels der Hefe Saccharomyces cerevisiae [Influencing the ergosterol metabolism of the yeast Saccharomyces cerevisiae by molecular biological means], Shaker Verlag Aachen, 1999, pages 59 to 66, it is known that increasing the rate of expression of HMG-CoA reductase alone, without interrupting the downstream metabolic flow as in EP 486 290, merely leads to a slight increase in the content of early sterols and of squalene, while the content of later sterols such as ergosterol does not change substantially and, in the case of ergosterol, even tendentially decreases.

WO 99/16886 describes a method for preparing ergosterol in yeasts which overexpress a combination of genes tHMG, ERG9, SAT1 and ERG1.

Tainaka et al., J, Ferment. Bioeng. 1995, 79, 64-66, further describe that overexpression of ERG11 (lanosterol C14-demethylase) leads to accumulation of 4,4-dimethylzymosterol but not of ergosterol. Compared to the wild type, the transformant showed an increase in the zymosterol content by a factor of from 1.1 to 1.47, depending on fermentation conditions.

Avruch et al, Can. J. Biochem 1976, 54(7), 657-665 and Xu et al, Biochem. Biophys. Res. Commun. 1988, 155(1), 509-517 describe that it is possible to detect, apart from zymosterol, also traces of cholesterol by specifically inhibiting C24-methyltransferase and also by a mutation in the gene locus erg6 in S. cerevisiae.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates the vector denoted pUG6-tHMG.

FIG. 2 illustrates the vector denoted pUG6-ERG1.

FIG. 3 illustrates the vector denoted pUG6-ERG11.

FIG. 4 illustrates the vectors denoted pFlat3 and pFlat1.

FIG. 5 a illustrates the vectors denoted pFlat1-EBP and pFlat3-EBP.

FIG. 5 b illustrates the vector denoted pFlat3-SC5D.

FIG. 5 c illustrates the vector denoted pFlat1-Ebp.

FIG. 5 d illustrates the vector denoted pFlat4-D24R.

FIG. 6 illustrates the vector denoted pFlat4.

FIG. 7 illustrates the vector denoted pFlat4-ERG4.

It is an object of the present invention to provide a method for preparing 7-dehydrocholesterol and/or the biosynthetic intermediates and/or secondary products thereof, which method has advantageous properties such as a higher product yield.

We have found that this object is achieved by a method for preparing 7-dehydrocholesterol and/or the biosynthetic intermediates and/or secondary products thereof, in which organisms are cultured which have, compared to the wild type, an increased activity of at least one of the activities selected from the group consisting of Δ8-Δ7-isomerase activity, Δ5-desaturase activity and Δ24-reductase activity.

An increased activity compared to the wild type means, in the case of the starting organism not having said activity, that said activity is caused. In the case of the starting organism already having said activity, an increased activity compared to the wild type means an activity increased by a percentage.

Δ8-Δ7-Isomerase activity means the enzyme activity of a Δ8-Δ7-isomerase, also referred to as Δ8-Δ7-sterol isomerase.

A Δ8-Δ7-isomerase means a protein which has the enzyme activity of converting zymosterol to cholesta-7,24-dienol.

Accordingly, Δ8-Δ7-isomerase activity means the amount of zymosterol converted or the amount of cholesta-7,24-dienol formed by the protein Δ8-Δ7-isomerase in a particular time.

In the case of an increased Δ8-Δ7-isomerase activity compared to the wild type, thus the amount of zymosterol converted or the amount of cholesta-7,24-dienol formed by the protein Δ8-Δ7-isomerase in a particular time is increased in comparison with the wild type.

This increase in Δ8-Δ7-isomerase activity is preferably at least 5%, further preferably at least 20%, further preferably at least 50%, further preferably at least 100%, more preferably at least 300%, still more preferably at least 500%, in particular at least 600%, of the Δ8-Δ7-isomerase activity of the wild type.

Δ5-Desaturase activity means the enzyme activity of a Δ5-desaturase, also referred to as lathosterol 5-desaturase or sterol C5-desaturase.

A Δ5-desaturase means a protein which has the enzyme activity of converting cholesta-7,24-dienol to cholesta-5,7,24-trienol.

Accordingly, Δ5-desaturase activity means the amount of cholesta-7,24-dienol converted or the amount of cholesta-5,7,24-trienol formed by the protein Δ5-desaturase in a particular time.

In the case of an increased Δ5-desaturase activity compared to the wild type, thus the amount of cholesta-7,24-dienol converted or the amount of cholesta-5,7,24-trienol formed by the protein Δ5-desaturase in a particular time is increased in comparison with the wild type.

This increase in Δ5-desaturase activity is preferably at least 5%, further preferably at least 20%, further preferably at least 50%, further preferably at least 100%, more preferably at least 300%, still more preferably at least 500%, in particular at least 600%, of the Δ5-desaturase activity of the wild type.

Δ24-Reductase activity means the enzyme activity of a Δ24-reductase, also referred to as 24-dehydrocholesterol reductase.

A Δ24-reductase means a protein which has the enzyme activity of converting the double bond between C24 and C25 of cholesterol compounds to a single bond, for example converting cholesta-5,7,24-trienol to 7-dehydrocholesterol or zymosterol to lathosterol or cholesta-7,24-dienol to cholesta-7-enol.

Accordingly, Δ24-reductase activity means preferably the amount of cholesta-5,7,24-trienol converted or the amount of 7-dehydrocholesterol formed by the protein Δ24-reductase in a particular time.

In the case of an increased Δ24-reductase activity compared to the wild type, thus the amount of cholesta-5,7,24-trienol converted or the amount of 7-dehydrocholesterol formed by the protein Δ24-reductase in a particular time is increased in comparison with the wild type.

This increase in Δ24-reductase activity is preferably at least 5%, further preferably at least 20%, further preferably at least 50%, further preferably at least 100%, more preferably at least 300%, still more preferably at least 500%, in particular at least 600%, of the Δ24-reductase activity of the wild type.

A wild type means the corresponding not genetically modified starting organism. Preferably and, in particular in those cases in which the organism or the wild type cannot be classified unambiguously, wild type means a reference organism for increasing the Δ8-Δ7-isomerase activity, increasing the Δ5-desaturase activity, increasing the Δ24-reductase activity, reducing the C24-methyltransferase activity described below, reducing the Δ22-desaturase activity described below, increasing the HMG-CoA-reductase activity described below, increasing the lanosterol C14-demethylase activity described below, increasing the squalene-epoxidase activity described below, increasing the squalene-synthetase activity described below and increasing the sterol-acyltransferase activity described below and also for increasing the content of 7-dehydrocholesterol and/or of the biosynthetic intermediates and/or secondary products thereof. This reference organism is preferably the yeast strain Saccharomyces cerevisiae AH22.

In the method of the invention, organisms are cultured which, compared to the wild type, have an increased activity of at least one of the activities selected from the group consisting of Δ8-Δ7-isomerase activity, Δ5-desaturase activity and Δ24-reductase activity.

In a preferred embodiment, organisms are cultured which, compared to the wild type, have an increased Δ8-Δ7-isomerase activity, Δ5-desaturase activity or Δ24-reductase activity.

In a particularly preferred embodiment of the method of the invention, the organisms have, compared to the wild type, an increased activity of at least two of the activities selected from the group consisting of Δ8-Δ7-isomerase activity, Δ5-desaturase activity and Δ24-reductase activity.

Particularly preferred combinations are Δ8-Δ7-isomerase activity and Δ5-desaturase activity, increased in comparison to the wild type, Δ8-Δ7-isomerase activity and Δ24-reductase activity, increased in comparison to the wild type, and Δ5-desaturase activity and Δ24-reductase activity, increased in comparison with the wild type.

In a very particularly preferred embodiment of the method of the invention, the organisms have, compared to the wild type, an increased Δ8-Δ7-isomerase activity, Δ5-desaturase activity and Δ24-reductase activity.

The Δ8-Δ7-isomerase activity, Δ5-desaturase activity and Δ24-reductase activity and also the HMG-CoA-reductase activity, lanosterol C14-demethylase activity, squalene-epoxidase activity, squalene-synthetase activity and sterol-acyltransferase activity, which are described below, may be increased independently of one another in various ways, for example by eliminating inhibiting regulatory mechanisms at the expression and protein level or by increasing, compared to the wild type, gene expression of the corresponding nucleic acids, i.e. nucleic acids encoding a Δ8-Δ7-isomerase, Δ5-desaturase, Δ24-reductase, HMG-CoA reductase, lanosterol C14-demethylase, squalene epoxidase, squalene synthetase or sterol acyltransferase.

Likewise, gene expression of the corresponding nucleic acid may be increased compared to the wild type in various ways, for example by inducing the appropriate genes by activators, i.e. by inducing the Δ8-Δ7-isomerase gene, the Δ5-desaturase gene, the Δ24-reductase gene, the HMG-CoA-reductase gene, the lanosterol C14-demethylase gene, the squalene-epoxidase gene, the squalene-synthetase gene or the sterol-acyltransferase gene by activators, or by introducing one or more gene copies of the appropriate nucleic acids, i.e. by introducing one or more nucleic acids encoding a Δ8-Δ7-isomerase, Δ5-desaturase, Δ24-reductase, HMG-CoA reductase, lanosterol C14-demethylase, squalene epoxidase, squalene synthetase or sterol acyltransferase into the organism.

Increasing the gene expression of a nucleic acid encoding a Δ8-Δ7-isomerase, Δ5-desaturase, Δ24-reductase, HMG-CoA reductase, lanosterol C14-demethylase, squalene epoxidase, squalene synthetase or sterol acyltransferase means according to the invention also manipulation of the expression of endogenous Δ8-Δ7-isomerases, Δ5-desaturases, Δ24-reductases, HMG-CoA reductases, lanosterol C14-demethylases, squalene epoxidases, squalene synthetases or sterol acyltransferases, which are intrinsic to the organism, in particular to the yeasts.

This may be achieved, for example, by modifying the promoter DNA sequence of genes coding for Δ8-Δ7-isomerase, Δ5-desaturase, Δ24-reductase, HMG-CoA reductase, lanosterol C14-demethylase, squalene epoxidase, squalene synthetase or sterol acyltransferase. Such a modification which causes an increased rate of expression of the relevant gene may be carried out, for example, by deleting or inserting DNA sequences.

As described above, it is possible to modify expression of the endogenous Δ8-Δ7-isomerase, Δ5-desaturase, Δ24-reductase, HMG-CoA reductase, lanosterol C14-demethylase, squalene epoxidase, squalene synthetase or sterol acyltransferase by applying exogenous stimuli. This may be carried out using particular physiological conditions, i.e. by applying foreign substances.

Furthermore, a modified or increased expression of endogenous Δ8-Δ7-isomerase, Δ5-desaturase, Δ24-reductase, HMG-CoA reductase, lanosterol C14-demethylase, squalene epoxidase, squalene synthetase or sterol acyltransferase genes may be achieved by interaction of a regulatory protein which is not present in the untransformed organism with the promoter of said genes.

A regulator of this type may be a chimeric protein which consists of a DNA-binding domain and a transcriptional activator domain, as described, for example, in WO 96/06166.

In a preferred embodiment, the Δ8-Δ7-isomerase activity is increased compared to the wild type by increasing the gene expression of a nucleic acid encoding a Δ8-Δ7-isomerase.

In a further preferred embodiment, gene expression of a nucleic acid encoding a Δ8-Δ7-isomerase is increased by introducing into the organism one or more nucleic acids encoding a Δ8-Δ7-isomerase.

For this purpose, it is possible to use in principle any Δ8-Δ7-isomerase gene, i.e. any nucleic acid encoding a Δ8-Δ7-isomerase.

In the case of genomic Δ8-Δ7-isomerase nucleic acid sequences from eukaryotic sources, which contain introns, preferably already processed nucleic acid sequences such as the corresponding cDNAs are to be used, if the host organism is unable to or cannot be enabled to express the appropriate Δ8-Δ7-isomerase.

Examples of Δ8-Δ7-isomerase genes are nucleic acids encoding a murine Δ8-Δ7-isomerase (nucleic acid: Seq. ID. No. 1, protein: Seq. ID. No. 2) or a human Δ8-Δ7-isomerase (nucleic acid: Seq. ID. No. 3, protein: Seq. ID. No. 4) (Braverman, N. et al., (1999): Mutations in the gene encoding

3β-hydroxysteroid-Δ8,Δ7-isomerase cause X-linked dominant Conradi-Hunermann syndrome, Nat. Genet. 22(3), 291-294), or else nucleic acids encoding proteins which have the activity of a Δ8-Δ7-isomerase, for example due to a broad substrate specificity, such as, for example, nucleic acids encoding a C8-isomerase Saccharomyces cerevisiae (ERG2) (Nucleic acid: Seq. ID. No. 5, protein: Seq. ID. No. 6) (Ashman, W. H. et al. (1991): Cloning and disruption of the yeast C-8 sterol isomerase gene. Lipids. August; 26(8):628-32).

In this preferred embodiment, thus at least one further Δ8-Δ7-isomerase gene is present in the transgenic organisms of the invention, compared to the wild type.

The number of Δ8-Δ7-isomerase genes in the transgenic organisms of the invention is at least two, preferably more than two, particularly preferably more than three and very particularly preferably more than five.

All of the nucleic acids mentioned in the description may be, for example, an RNA sequence, DNA sequence or cDNA sequence.

Preferred Δ8-Δ7-isomerase genes are nucleic acids encoding proteins which have a high substrate specificity for zymosterol. Therefore, preference is given in particular to Δ8-Δ7-isomerase genes and to the corresponding Δ8-Δ7-isomerases of mammals and to the functional equivalents thereof.

Accordingly, preference is given to using in the above-described method nucleic acids which encode proteins comprising the amino acid sequence SEQ. ID. NO. 2 or a sequence derived from this sequence by substitution, insertion or deletion of amino acids, which is at least 30%, preferably at least 50%, more preferably at least 70%, still more preferably at least 90%, most preferably at least 95%, identical at the amino acid level with the sequence SEQ. ID. NO. 2, and having the enzyme property of a Δ8-Δ7-isomerase.

The sequence SEQ. ID. NO. 2 represents the amino acid sequence of Mus musculus Δ8-Δ7-isomerase.

Further examples of Δ8-Δ7-isomerases and Δ8-Δ7-isomerase genes can readily be found, for example, for various organisms whose genomic sequence is known by comparing the homology of the amino acid sequences or the corresponding backtranslated nucleic acid sequences from databases with the SeQ ID. NO. 2.

The Homo sapiens Δ8-Δ7-isomerase (Seq. ID. No. 4), for example, is 74% identical to the Mus musculus Δ8-Δ7-isomerase (Seq. ID. No. 2).

Further examples of Δ8-Δ7-isomerases and Δ8-Δ7-isomerase genes can furthermore readily be found for various organisms whose genomic sequence is unknown, for example starting from the sequence SEQ. ID. No. 1, by hybridization techniques and PCR techniques in a manner known per se.

The term “substitution” means in the description the replacement of one or more amino acids by one or more amino acids. Preference is given to carrying out “conservative” replacements in which the replacing amino acid has a similar property to that of the original amino acid, for example replacement of Glu by Asp, Gln by Asn, Val by Ile, Leu by Ile, Ser by Thr.

A deletion is the replacement of an amino acid by a direct bond. Preferred positions for deletions are the polypeptide termini and the linkages between the individual protein domains.

Insertions are introductions of amino acids into the polypeptide chain, with a direct bond formally being replaced by one or more amino acids.

Identity between two proteins means identity of the amino acids over the in each case entire length of the protein, in particular the identity which is calculated by comparison with the aid of the Lasergene software from DNASTAR Inc., Madison, Wis. (USA), using the Clustal method (Higgins D G, Sharp P M. Fast and sensitive multiple sequence alignments on a microcomputer. Comput Appl. Biosci. 1989 April; 5(2):151-1) and setting the following parameters: TABLE-US-00001 Multiple alignment parameter: Gap penalty 10 Gap length penalty 10 Pairwise alignment parameter: K-tuple 1 Gap penalty 3 Window 5 Diagonals saved 5

Accordingly, a protein which is at least 30% identical at the amino acid level with the sequence SEQ. ID. NO. 2 means a protein which is at least 30% identical when comparing its sequence with the sequence SEQ. ID. NO. 2, in particular according to the above program algorithm with the above set of parameters.

In a further, particularly preferred embodiment, the Δ8-Δ7-isomerase activity is increased by introducing into organisms nucleic acids which encode proteins comprising the amino acid sequence of Mus musculus Δ8-Δ7-isomerase (SEQ. ID. NO. 2).

Suitable nucleic acid sequences can be obtained, for example, by backtranslating the polypeptide sequence according to the genetic code.

Preference is given to using for this those codons which are frequently used according to the organism-specific codon usage. Said codon usage can readily be determined on the basis of computer analyses of other known genes of the organisms in question.

If the protein is to be expressed in yeast, for example, it is often advantageous to use the codon usage of yeast for backtranslation.

In a particularly preferred embodiment, a nucleic acid comprising the sequence SEQ. ID. NO. 1 is introduced into the organism.

The sequence SEQ. ID. NO. 1 represents the Mus musculus cDNA which encodes the Δ8-Δ7-isomerase of the sequence SEQ ID NO. 2.

Furthermore, all of the Δ8-Δ7-isomerase genes mentioned above can be prepared in a manner known per se by chemical synthesis from the nucleotide building blocks, for example by fragment condensation of individual overlapping complementary nucleic acid building blocks of the double helix. The chemical synthesis of oligonucleotides may be carried out, for example, in a known manner according to the phosphoramidite method (Voet, Voet, 2nd edition, Wiley Press New York, pages 896-897). Annealing of synthetic oligonucleotides and filling-in of gaps with the aid of the Klenow fragment of DNA polymerase and the ligation reactions and also general cloning methods are described in Sambrook et al. (1989), Molecular cloning: A laboratory manual, Cold Spring Harbor Laboratory Press.

In a preferred embodiment, the Δ5-desaturase activity is increased compared to the wild type by increasing the gene expression of a nucleic acid encoding a Δ5-desaturase.

In a further preferred embodiment, gene expression of a nucleic acid encoding a Δ5-desaturase is increased by introducing into the organism one or more nucleic acids encoding a Δ5-desaturase.

For this purpose, it is possible to use in principle any Δ5-desaturase gene, i.e. any nucleic acid encoding a Δ5-desaturase.

In the case of genomic Δ5-desaturase nucleic acid sequences from eukaryotic sources, which contain introns, preferably already processed nucleic acid sequences such as the corresponding cDNAs are to be used, if the host organism is unable to or cannot be enabled to express the appropriate Δ5-desaturase.

Examples of Δ5-desaturase genes are nucleic acids encoding a murine Δ5-desaturase (nucleic acid: Seq. ID. No. 7, protein: Seq. ID. No. 8) or a human Δ5-desaturase (nucleic acid: Seq. ID. No. 9, protein: Seq. ID. No. 10) (Nishi, S. et al., (2000): cDNA cloning of the mammalian sterol C5-desaturase and the expression in yeast mutant. Biochim. Biophys. Acta, 1490, (1-2), 106-108), or else nucleic acids encoding proteins which have the activity of a Δ5-desaturase, for example due to a broad substrate specificity, such as, for example, nucleic acids encoding a Saccharomyces cerevisiae C5-desaturase (ERG3) (nucleic acid: Seq. ID. No. 11, protein: Seq. ID. No. 12), (Arthington, B. A. et al. (1991): Cloning, disruption and sequence of the gene encoding yeast C-5 sterol desaturase. Gene. June 15; 102(1):39-44.).

In this preferred embodiment, thus at least one further Δ5-desaturase gene is present in the transgenic organisms of the invention, compared to the wild type.

The number of Δ5-desaturase genes in the transgenic organisms of the invention is at least two, preferably more than two, particularly preferably more than three and very particularly preferably more than five.

Preferred Δ5-desaturase genes are nucleic acids encoding proteins which have a high substrate specificity for cholesta-7,24-dienol. Therefore, preference is given in particular to Δ5-desaturase genes and to the corresponding Δ5-desaturases of mammals and to the functional equivalents thereof.

Accordingly, preference is given to using in the above-described method nucleic acids which encode proteins comprising the amino acid sequence SEQ. ID. NO. 8 or a sequence derived from this sequence by substitution, insertion or deletion of amino acids, which is at least 30%, preferably at least 50%, more preferably at least 70%, still more preferably at least 90%, most preferably at least 95%, identical at the amino acid level with the sequence SEQ. ID. NO. 8, and having the enzyme property of a Δ5-desaturase.

The sequence SEQ. ID. NO. 8 represents the amino acid sequence of Mus musculus Δ5-desaturase.

Further examples of Δ5-desaturase and Δ5-desaturase genes can readily be found, for example, for various organisms whose genomic sequence is known by comparing the homology of the amino acid sequences or the corresponding backtranslated nucleic acid sequences from databases with the SeQ ID. NO. 2.

The Homo sapiens Δ5-desaturase (Seq. ID. No. 10), for example, is 84% identical to Mus musculus Δ5-desaturase (Seq. ID. No. 8).

Further examples of Δ5-desaturases and Δ5-desaturase genes can furthermore readily be found for various organisms whose genomic sequence is unknown, for example starting from the sequence SEQ. ID. No. 7, by hybridization techniques and PCR techniques in a manner known per se.

Accordingly, a protein which is at least 30% identical at the amino acid level with the sequence SEQ. ID. NO. 8 means a protein which is at least 30% identical when comparing its sequence with the sequence SEQ. ID. NO. 8, in particular according to the above program algorithm with the above set of parameters.

In a further, particularly preferred embodiment, the Δ5-desaturase activity is increased by introducing into organisms nucleic acids which encode proteins comprising the amino acid sequence of Mus musculus Δ5-desaturase (SEQ. ID. NO. 8).

Suitable nucleic acid sequences can be obtained, for example, by backtranslating the polypeptide sequence according to the genetic code.

Preference is given to using for this those codons which are frequently used according to the organism-specific codon usage. Said codon usage can readily be determined on the basis of computer analyses of other known genes of the organisms in question.

If the protein is to be expressed in yeast, for example, it is often advantageous to use the codon usage of yeast for backtranslation.

In a particularly preferred embodiment, a nucleic acid comprising the sequence SEQ. ID. NO. 7 is introduced into the organism.

The sequence SEQ. ID. NO. 7 represents the Mus musculus cDNA which encodes the Δ5-desaturase of the sequence SEQ ID NO. 8.

Furthermore, all of the Δ5-desaturase genes mentioned above can be prepared in a manner known per se by chemical synthesis from the nucleotide building blocks, for example by fragment condensation of individual overlapping complementary nucleic acid building blocks of the double helix. The chemical synthesis of oligonucleotides may be carried out, for example, in a known manner according to the phosphoramidite method (Voet, Voet, 2nd edition, Wiley Press New York, pages 896-897). Annealing of synthetic oligonucleotides and filling-in of gaps with the aid of the Klenow fragment of DNA polymerase and the ligation reactions and also general cloning methods are described in Sambrook et al. (1989), Molecular cloning: A laboratory manual, Cold Spring Harbor Laboratory Press.

In a preferred embodiment, the Δ24-reductase activity is increased compared to the wild type by increasing the gene expression of a nucleic acid encoding a Δ24-reductase.

In a further preferred embodiment, gene expression of a nucleic acid encoding a Δ24-reductase is increased by introducing into the organism one or more nucleic acids encoding a Δ24-reductase.

For this purpose, it is possible to use in principle any Δ24-reductase gene, i.e. any nucleic acid encoding a Δ24-reductase.

In the case of genomic Δ24-reductase nucleic acid sequences from eukaryotic sources, which contain introns, preferably already processed nucleic acid sequences such as the corresponding cDNAs are to be used, if the host organism is unable to or cannot be enabled to express the appropriate Δ24-reductase.

Examples of Δ24-reductase genes are nucleic acids encoding a murine Δ24-reductase (nucleic acid: Seq. ID. No. 13, protein: Seq. ID. No. 14) or a human Δ24-reductase (nucleic acid: Seq. ID. No. 15, protein: Seq. ID. No. 16) (Waterham, H. R. et al.: Mutations in the 3β-Hydroxysterol Δ24-Reductase Gene Cause Desmosterolosis, an Autosomal Recessive Disorder of Cholesterol Biosynthesis, Am. J. Hum. Genet. 69 (4), 685-694 (2001)), or else nucleic acids encoding proteins which have the activity of a Δ24-reductase, for example due to a broad substrate specificity, such as, for example, nucleic acids encoding a Saccharomyces cerevisiae Δ24-reductase (ERG4) (nucleic acid: Seq. ID. No. 17, protein: Seq. ID. No. 18) (Lai, M. H. et al., (1994): The identification of a gene family in the Saccharomyces cerevisiae ergosterol biosynthesis pathway. Gene. March 11; 140(1):41-9).

In this preferred embodiment, thus at least one further Δ24-reductase gene is present in the transgenic organisms of the invention, compared to the wild type.

The number of Δ24-reductase genes in the transgenic organisms of the invention is at least two, preferably more than two, particularly preferably more than three and very particularly preferably more than five.

Preferred Δ24-reductase genes are nucleic acids encoding proteins which have a high substrate specificity for cholesta-5,7,24-trienol. Therefore, preference is given in particular to Δ24-reductase genes and to the corresponding Δ24-reductase of mammals and to the functional equivalents thereof.

Accordingly, preference is given to using in the above-described method nucleic acids which encode proteins comprising the amino acid sequence SEQ. ID. NO. 14 or a sequence derived from this sequence by substitution, insertion or deletion of amino acids, which is at least 30%, preferably at least 50%, more preferably at least 70%, still more preferably at least 90%, most preferably at least 95%, identical at the amino acid level with the sequence SEQ. ID. NO. 14, and having the enzyme property of a Δ24-reductase.

The sequence SEQ. ID. NO. 14 represents the amino acid sequence of Mus musculus Δ24-reductase.

Further examples of Δ24-reductases and Δ24-reductase genes can readily be found, for example, for various organisms whose genomic sequence is known by comparing the homology of the amino acid sequences or the corresponding backtranslated nucleic acid sequences from databases with the SeQ ID. NO. 14.

The Homo sapiens Δ24-reductase (Seq. ID. No. 16), for example, is 96% identical to Mus musculus Δ24-reductase (Seq. ID. No. 14).

Further examples of Δ24-reductases and Δ24-reductase genes can furthermore readily be found for various organisms whose genomic sequence is unknown, for example starting from the sequence SEQ. ID. No. 13, by hybridization techniques and PCR techniques in a manner known per se.

Accordingly, a protein which is at least 30% identical at the amino acid level with the sequence SEQ. ID. NO. 14 means a protein which is at least 30% identical when comparing its sequence with the sequence SEQ. ID. NO. 14, in particular according to the above program algorithm with the above set of parameters.

In a further, particularly preferred embodiment, the Δ24-reductase activity is increased by introducing into organisms nucleic acids which encode proteins comprising the amino acid sequence of Mus musculus Δ24-reductase (SEQ. ID. NO. 14).

Suitable nucleic acid sequences can be obtained, for example, by backtranslating the polypeptide sequence according to the genetic code.

Preference is given to using for this those codons which are frequently used according to the organism-specific codon usage. Said codon usage can readily be determined on the basis of computer analyses of other known genes of the organisms in question.

If the protein is to be expressed in yeast, for example, it is often advantageous to use the codon usage of yeast for backtranslation.

In a particularly preferred embodiment, a nucleic acid comprising the sequence SEQ. ID. NO. 13 is introduced into the organism.

The sequence SEQ. ID. NO. 13 represents the Mus musculus genomic DNA which encodes the Δ24-reductase of the sequence SEQ ID NO. 14.

Furthermore, all of the Δ24-reductase genes mentioned above can be prepared in a manner known per se by chemical synthesis from the nucleotide building blocks, for example by fragment condensation of individual overlapping complementary nucleic acid building blocks of the double helix. The chemical synthesis of oligonucleotides may be carried out, for example, in a known manner according to the phosphoramidite method (Voet, Voet, 2nd edition, Wiley Press New York, pages 896-897). Annealing of synthetic oligonucleotides and filling-in of gaps with the aid of the Klenow fragment of DNA polymerase and the ligation reactions and also general cloning methods are described in Sambrook et al. (1989), Molecular cloning: A laboratory manual, Cold Spring Harbor Laboratory Press.

In a further preferred embodiment of the method of the invention, organisms are cultured which have, compared to the wild type, a reduced activity of at least one of the activities selected from the group consisting of C24-methyltransferase activity and Δ22-desaturase activity in addition to the above-described genetic modifications.

In a further particularly preferred embodiment, organisms are cultured which have, compared to the wild type, a reduced C24-methyltransferase activity and a reduced Δ22-desaturase activity in addition to the above-described genetic modifications.

A reduced activity means both the reduced and the complete elimination of said activity. Reducing an activity therefore also comprises a reduction in the amount of the corresponding protein in the organism up to a complete absence of the corresponding protein, which can be tested, for example, via missing detectability of the corresponding enzyme activity or missing immunological detectability of the corresponding proteins.

A C24-methyltransferase activity means the enzyme activity of a C24-methyltransferase.

A C24-methyltransferase means a protein which has the enzyme activity of converting zymosterol to fecosterol (ergosta-8,24(28)dienol).

Accordingly, C24-methyltransferase activity means the amount of zymosterol converted or the amount of fecosterol formed by the protein C24-methyltransferase in a particular time.

In the case of a reduced C24-methyltransferase activity compared to the wild type, thus the amount of zymosterol converted or the amount of fecosterol formed by the protein C24-methyltransferase in a particular time is reduced in comparison with the wild type.

The C24-methyltransferase activity is reduced preferably to at least 90%, further preferably to at least 70%, further preferably to at least 50%, further preferably to at least 30%, more preferably to at least 10%, still more preferably to at least 5%, in particular to 0%, of the C24-methyltransferase activity of the wild type. Therefore, particular preference is given to eliminating the C24-methyltransferase activity in the organism.

Δ22-desaturase activity means the enzyme activity of a Δ22-desaturase.

A Δ22-desaturase means a protein which has the enzyme activity of converting ergosta-5,7-dienol to ergosta-5,7,22,24-tetraen-3β.-ol.

Accordingly, Δ22-desaturase activity means the amount of ergosta-5,7-dienol converted or the amount of ergosta-5,7,22,24-tetraen-3β.-ol formed by the protein Δ22-desaturase in a particular time.

In the case of a reduced Δ22-desaturase activity compared to the wild type, thus the amount of ergosta-5,7-dienol converted or the amount of ergosta-5,7,22,24-tetraen-3β.-ol formed by the protein Δ22-desaturase in a particular time is reduced in comparison with the wild type.

The Δ22-desaturase activity is reduced preferably to at least 90%, further preferably to at least 70%, further preferably to at least 50%, further preferably to at least 30%, more preferably to at least 10%, still more preferably to at least 5%, in particular to 0%, of the Δ22-desaturase activity of the wild type. Therefore, particular preference is given to eliminating the Δ22-desaturase activity in the organism.

The reduction in C24-methyltransferase activity and/or Δ22-desaturase activity may be carried out independently of one another by different cell-biological mechanisms, for example by inhibiting the corresponding activity at the protein level, for example by adding inhibitors of the corresponding enzymes or by reducing gene expression of the corresponding nucleic acids encoding a C24-methyltransferase or Δ22-desaturase, compared to the wild type.

In a particularly preferred embodiment of the method of the invention, the C24-methyltransferase activity and/or the Δ22-desaturase activity are reduced compared to the wild type by reducing the gene expression of the corresponding nucleic acids encoding a C24-methyltransferase or Δ22-desaturase.

Likewise, gene expression of the nucleic acids encoding a C24-methyltransferase or Δ22-desaturase may be reduced compared to the wild type in various ways, for example by

a) introducing nucleic acid sequences which can be transcribed to an antisense nucleic acid sequence which is capable of inhibiting the C24-methyltransferase activity and/or Δ22-desaturase activity, for example by inhibiting the expression of endogenous C24-methyltransferase and/or Δ22-desaturase activity, b) overexpression of homologous C24-methyltransferase nucleic acid sequences and/or Δ22-desaturase nucleic acid sequences, which leads to cosuppression, c) introducing nonsense mutations into the endogene by means of introducing RNA/DNA oligonucleotides into the organism, d) introducing specific DNA-binding factors, for example factors of the zinc finger transcription factor type, which cause a reduction in gene expression or e) generating knockout mutants, for example with the aid of T-DNA mutagenesis or homologous recombination.

In a preferred embodiment of the method of the invention, gene expression of the nucleic acids encoding a C24-methyltransferase or Δ22-desaturase is reduced by generating knockout mutants, particularly preferably by homologous recombination.

Therefore, preference is given to using an organism which has no functional C24-methyltransferase gene and/or Δ22-desaturase gene.

In a preferred embodiment, knockout mutants are generated, i.e. the C24-methyltransferase-gene target locus and/or the Δ22-desaturase-gene target locus are deleted with simultaneous integration of an expression cassette containing at least one of the nucleic acids described above or below, which encode a protein whose activity is increased in comparison with the wild type, by homologous recombination.

For this purpose, it is possible to use nucleic acid constructs which, in addition to the expression cassettes described below which contain promoter, coding sequence and, where appropriate, terminator and in addition to a selection marker at the 3′ and 5′ ends, described below, contain nucleic acid sequences which are identical to nucleic acid sequences at the start and the end of the gene to be deleted.

After selection by recombinase systems, the selection marker may preferably be removed again, for example via loxP signals at the 3′ and 5′ ends of the selection marker, using a Cre recombinase (Cre-loxP system).

In the preferred organism Saccharomyces cerevisiae, the C24-methyltransferase gene is the gene ERG6 (SEQ. ID. NO. 19). SEQ. ID. NO. 20 represents the corresponding Saccharomyces cerevisiae C24-methyltransferase (Hardwick, K. G. et al.: SED6 is identical to ERG6, and encodes a putative methyltransferase required for ergosterol synthesis. Yeast. February; 10(2):265-9).

In the preferred organism Saccharomyces cerevisiae, the Δ22-desaturase gene is the gene ERG5 (SEQ. ID. NO. 21). SEQ. ID. NO. 22 represents the corresponding Saccharomyces cerevisiae Δ22-desaturase (Skaggs, B. A. et al, Cloning and characterization of the Saccharomyces cerevisiae C-22 sterol desaturase gene, encoding a second cytochrome P-450 involved in ergosterol biosynthesis, Gene. 1996 Feb. 22; 169(1):105-9).

In a further preferred embodiment of the method of the invention, organisms are cultured which have, in addition to the above-described modifications, an increased activity of at least one of the activities selected from the group consisting of HMG-CoA-reductase activity, lanosterol-C14-demethylase activity, squalene-epoxidase activity, squalene-synthetase activity and sterol-acyltransferase activity, compared to the wild type.

HMG-CoA-reductase activity means the enzyme activity of an HMG-CoA reductase (3-hydroxy-3-methylglutaryl-coenzyme-A reductase).

HMG-CoA reductase means a protein which has the enzyme activity of converting 3-hydroxy-3-methylglutaryl-coenzyme A to mevalonate.

Accordingly, HMG-CoA-reductase activity means the amount of 3-hydroxy-3-methylglutaryl-coenzyme A converted or the amount of mevalonate formed by the protein HMG-CoA reductase in a particular time.

In the case of an increased HMG-CoA-reductase activity compared to the wild type, thus the amount of 3-hydroxy-3-methylglutaryl-coenzyme A converted or the amount of mevalonate formed by the protein HMG-CoA reductase in a particular time is increased in comparison with the wild type.

This increase in HMG-CoA-reductase activity is preferably at least 5%, further preferably at least 20%, further preferably at least 50%, further preferably at least 100%, more preferably at least 300%, still more preferably at least 500%, in particular at least 600%, of the HMG-CoA-reductase activity of the wild type.

Lanosterol C14-demethylase activity means the enzyme activity of a lanosterol C14-demethylase.

Lanosterol C14-demethylase means a protein which has the enzyme activity of converting lanosterol to 4,4-dimethylcholesta-8,14,24-trienol.

Accordingly, lanosterol C14-demethylase activity means the amount of lanosterol converted or the amount of 4,4-dimethylcholesta-8,14,24-trienol formed by the protein lanosterol C14-demethylase in a particular time.

In the case of an increased lanosterol C14-demethylase activity compared to the wild type, thus the amount of lanosterol converted or the amount of 4,4-dimethylcholesta-8,14,24-trienol formed by the protein lanosterol C14-demethylase in a particular time is increased in comparison with the wild type.

This increase in lanosterol C14-demethylase activity is preferably at least 5%, further preferably at least 20%, further preferably at least 50%, further preferably at least 100%, more preferably at least 300%, still more preferably at least 500%, in particular at least 600%, of the lanosterol C14-demethylase activity of the wild type.

Squalene-epoxidase activity means the enzyme activity of a squalene epoxidase.

Squalene epoxidase means a protein which has the enzyme activity of converting squalene to squalene epoxide.

Accordingly, squalene-epoxidase activity means the amount of squalene converted or the amount of squalene epoxide formed by the protein squalene epoxidase in a particular time.

In the case of an increased squalene-epoxidase activity compared to the wild type, thus the amount of squalene converted or the amount of squalene epoxide formed by the protein squalene epoxidase in a particular time is increased in comparison with the wild type.

This increase in squalene-epoxidase activity is preferably at least 5%, further preferably at least 20%, further preferably at least 50%, further preferably at least 100%, more preferably at least 300%, still more preferably at least 500%, in particular at least 600%, of the squalene-epoxidase activity of the wild type.

Squalene-synthetase activity means the enzyme activity of a squalene synthetase.

Squalene synthetase means a protein which has the enzyme activity of converting farnesyl-pyrophosphate to squalene.

Accordingly, squalene-synthetase activity means the amount of farnesyl-pyrophosphate converted or the amount of squalene formed by the protein squalene synthetase in a particular time.

In the case of an increased squalene-synthetase activity compared to the wild type, thus the amount of farnesyl-pyrophosphate converted or the amount of squalene formed by the protein squalene synthetase in a particular time is increased in comparison with the wild type.

This increase in squalene-synthetase activity is preferably at least 5%, further preferably at least 20%, further preferably at least 50%, further preferably at least 100%, more preferably at least 300%, still more preferably at least 500%, in particular at least 600%, of the squalene-synthetase activity of the wild type.

Sterol-acyltransferase activity means the enzyme activity of a sterol acyltransferase.

Sterol acyltransferase means a protein which has the enzyme activity of converting 7-dehydrocholesterol to corresponding acetylated 7-dehydrocholesterol.

Accordingly, sterol-acyltransferase activity means the amount of 7-dehydrocholesterol converted or the amount of acetylated 7-dehydrocholesterol formed by the protein sterol acyltransferase in a particular time.

In the case of an increased sterol-acyltransferase activity compared to the wild type, thus the amount of 7-dehydrocholesterol converted or the amount of acetylated 7-dehydrocholesterol formed by the protein sterol acyltransferase in a particular time is increased in comparison with the wild type.

This increase in sterol-acyltransferase activity is preferably at least 5%, further preferably at least 20%, further preferably at least 50%, further preferably at least 100%, more preferably at least 300%, still more preferably at least 500%, in particular at least 600%, of the sterol-acyltransferase activity of the wild type.

In a preferred embodiment, the HMG-CoA-reductase activity is increased compared to the wild type by increasing the gene expression of a nucleic acid encoding an HMG-CoA reductase.

In a particularly preferred embodiment of the method of the invention, gene expression of a nucleic acid encoding an HMG-CoA reductase is increased by introducing into the organism a nucleic acid construct comprising an HMG-CoA reductase-encoding nucleic acid whose expression in said organism is subject to a reduced regulation, in comparison with the wild type.

A reduced regulation in comparison with the wild type means a reduced regulation and, preferably, no regulation at the expression or protein level, in comparison with the above-defined wild type.

The reduced regulation may be achieved preferably by a promoter which is functionally linked with the coding sequence in the nucleic acid construct and which is subject to a reduced regulation in the organism, in comparison with the wild-type promoter.

For example, the medium ADH promoter in yeast is subject only to a reduced regulation and is therefore particularly preferred as promoter in the above-described nucleic acid construct.

This promoter fragment of the ADH12s promoter, also referred to as ADH1 hereinbelow, exhibits nearly constitutive expression (Ruohonen L, Penttila M, Keranen S. (1991) Optimization of Bacillus α-amylase production by Saccharomyces cerevisiae. Yeast. May-June; 7(4):337-462; Lang C, Looman A C. (1995) Efficient expression and secretion of Aspergillus niger RH5344 polygalacturonase in Saccharomyces cerevisiae. Appl Microbiol Biotechnol. December; 44(1-2):147-56) so that transcriptional regulation no longer proceeds via intermediates of ergosterol biosynthesis.

Other preferred promoters with reduced regulation are constitutive promoters such as, for example, the yeast TEF1 promoter, the yeast GPD promoter or the yeast PGK promoter (Mumberg D, Muller R, Funk M. (1995) Yeast vectors for the controlled expression of heterologous proteins in different genetic backgrounds. Gene. 1995 Apr. 14; 156(1):119-22; Chen C Y, Oppermann H, Hitzeman R A. (1984) Homologous versus heterologous gene expression in the yeast, Saccharomyces cerevisiae. Nucleic Acids Res. December 11; 12(23):8951-70).

In a further preferred embodiment, reduced regulation can be achieved by using as an HMG-CoA reductase-encoding nucleic acid a nucleic acid whose expression in the organism is subject to a reduced regulation, in comparison with the orthologous nucleic acid intrinsic to said organism.

Particular preference is given to using as an HMG-CoA reductase-encoding nucleic acid a nucleic acid which encodes only the catalytic region of HMG-CoA reductase (truncated (t-) HMG-CoA reductase). This nucleic acid (t-HMG), described in EP 486 290 and WO 99/16886 encodes only the catalytically active part of HMG-CoA reductase, with the membrane domain responsible for regulation at the protein level missing. This nucleic acid is thus subject to a reduced regulation, in particular in yeast, and leads to an increase in gene expression of HMG-CoA reductase.

In a particularly preferred embodiment, nucleic acids are introduced, preferably via the above-described nucleic acid construct, which encode proteins comprising the amino acid sequence SEQ. ID. NO. 24 or a sequence derived from this sequence by substitution, insertion or deletion of amino acids, which is at least 30% identical at the amino acid level to the sequence SEQ ID. NO. 24, and having the enzyme property of an HMG-CoA reductase.

The sequence SEQ ID NO. 24 is the amino acid sequence of the truncated HMG-CoA reductase (t-HMG).

Further examples of HMG-CoA reductases and thus also of the t-HMG-CoA reductases reduced to the catalytic region or of the coding genes can readily be found, for example, for various organisms whose genomic sequence is known by comparing the homology of the amino acid sequences or of the corresponding backtranslated nucleic acid sequences from databases with the sequence SEQ ID. No. 24.

Further examples of HMG-CoA reductases and thus also of the t-HMG-CoA reductases reduced to the catalytic region and of the coding genes can furthermore readily be found for various organisms whose genomic sequence is unknown by hybridization techniques and PCR techniques in a manner known per se, for example starting from the sequence SEQ ID NO. 23.

Particular preference is given to using as a truncated HMG-CoA reductase-encoding nucleic acid a nucleic acid comprising the sequence SEQ ID NO. 23.

In a particularly preferred embodiment, the reduced regulation is achieved by using as an HMG-CoA reductase-encoding nucleic acid a nucleic acid whose expression in the organism is subject to a reduced regulation, in comparison with the orthologous nucleic acid intrinsic to said organism, and by using a promoter which is subject to a reduced regulation in said organism, in comparison with the wild-type promoter.

In a preferred embodiment, the lanosterol C14-demethylase activity is increased compared to the wild type by increasing the gene expression of a nucleic acid encoding a lanosterol C14-demethylase.

In a further preferred embodiment, gene expression of a nucleic acid encoding a lanosterol C14-demethylase is increased by introducing into the organism one or more nucleic acids encoding a lanosterol C14-demthylase.

For this purpose, it is possible to use in principle any lanosterol C14-demethylase gene (ERG11), i.e. any nucleic acids encoding a lanosterol C14-demethylase. In the case of genomic lanosterol C14-demethylase nucleic acid sequences from eukaryotic sources, which contain introns, already processed nucleic acid sequences such as the corresponding cDNAs are to be used preferably, if the host organism is unable to or cannot be enabled to express the appropriate lanosterol C14-demethylase.

Examples of lanosterol C14-demethylase genes are nucleic acids encoding a lanosterol C14-demethylase of Saccharomyces cerevisiae (Kalb V F, Loper J C, Dey C R, Woods C W, Sutter T R (1986) Isolation of a cytochrome P-450 structural gene from Saccharomyces cerevisiae. Gene 45(3):237-45), Candida albicans (Lamb D C, Kelly D E, Baldwin B C, Gozzo F, Boscott P, Richards W G, Kelly S L (1997) Differential inhibition of Candida albicans CYP51 with azole antifungal stereoisomers. FEMS Microbiol Lett 149(1):25-30), Homo sapiens (Stromstedt M, Rozman D, Waterman M R. (1996) The ubiquitously expressed human CYP51 encodes lanosterol 14 a-demethylase, a cytochrome P450 whose expression is regulated by oxysterols. Arch Biochem Biophys 1996 May 1; 329(1):73-81c) or Rattus norvegicus, Aoyama Y, Funae Y, Noshiro M, Horiuchi T, Yoshida Y. (1994) Occurrence of a P450 showing high homology to yeast lanosterol 14-demethylase (P450(14DM)) in the rat liver. Biochem Biophys Res Commun. June 30; 201(3):1320-6).

In this preferred embodiment, thus at least one further lanosterol C14-demethylase gene is present in the transgenic organisms of the invention, compared to the wild type.

The number of C14-demethylase genes in the transgenic organisms of the invention is at least two, preferably more than two, particularly preferably more than three and very particularly preferably more than five.

Preference is given to using in the above-described method nucleic acids which encode proteins comprising the amino acid sequence SEQ. ID. NO. 26 or a sequence derived from this sequence by substitution, insertion or deletion of amino acids, which is at least 30%, preferably at least 50%, more preferably at least 70%, still more preferably at least 90%, most preferably at least 95%, identical at the amino acid level with the sequence SEQ. ID. NO. 26, and having the enzyme property of a lanosterol C14-demethylase.

The sequence SEQ. ID. NO. 26 represents the amino acid sequence of Saccharomyces cerevisiae lanosterol C14-demethylase.

Further examples of lanosterol C14-demethylases and lanosterol C14-demethylase genes can readily be found, for example, for various organisms whose genomic sequence is known by comparing the homology of the amino acid sequences or the corresponding backtranslated nucleic acid sequences from databases with the SeQ ID. NO. 26.

Further examples of lanosterol C14-demethylases and lanosterol C14-demethylase genes can furthermore readily be found for various organisms whose genomic sequence is unknown, for example starting from the sequence SEQ. ID. No. 25, by hybridization techniques and PCR techniques in a manner known per se.

Accordingly, a protein which is at least 30% identical at the amino acid level with the sequence SEQ. ID. NO. 26 means a protein which is at least 30% identical when comparing its sequence with the sequence SEQ. ID. NO. 26, in particular according to the above program algorithm with the above set of parameters.

In another preferred embodiment, nucleic acids are introduced into organisms, which encode proteins comprising the amino acid sequence of Saccharomyces cerevisiae lanosterol C14-demethylase (SEQ. ID. NO. 26).

Suitable nucleic acid sequences can be obtained, for example, by backtranslating the polypeptide sequence according to the genetic code.

Preference is given to using for this those codons which are frequently used according to the organism-specific codon usage. Said codon usage can readily be determined on the basis of computer analyses of other known genes of the organisms in question.

If the protein is to be expressed in yeast, for example, it is often advantageous to use the codon usage of yeast for the backtranslation.

In a particularly preferred embodiment, a nucleic acid comprising the sequence SEQ. ID. NO. 25 is introduced into the organism.

The sequence SEQ. ID. NO. 25 represents the genomic DNA of Saccharomyces cerevisiae (ORF S0001049), which encodes the lanosterol C14-demethylase of the sequence SEQ ID NO. 26.

Furthermore, all of the lanosterol C14-demethylase genes mentioned above can be prepared in a manner known per se by chemical synthesis from the nucleotide building blocks, for example by fragment condensation of individual overlapping complementary nucleic acid building blocks of the double helix. The chemical synthesis of oligonucleotides may be carried out, for example, in a known manner according to the phosphoramidite method (Voet, Voet, 2nd edition, Wiley Press New York, pages 896-897). Annealing of synthetic oligonucleotides and filling-in of gaps with the aid of the Klenow fragment of DNA polymerase and the ligation reactions and also general cloning methods are described in Sambrook et al. (1989), Molecular cloning: A laboratory manual, Cold Spring Harbor Laboratory Press.

In a preferred embodiment, the squalene-epoxidase activity is increased compared to the wild type by increasing the gene expression of a nucleic acid encoding a squalene epoxidase.

In a further preferred embodiment, gene expression of a nucleic acid encoding a squalene epoxidase is increased by introducing into the organism one or more nucleic acids encoding a squalene epoxidase.

For this purpose, it is possible to use in principle any squalene-epoxidase gene (ERG1), i.e. any nucleic acids encoding a squalene epoxidase. In the case of genomic squalene epoxidase nucleic acid sequences from eukaryotic sources, which contain introns, already processed nucleic acid sequences such as the corresponding cDNAs are to be used preferably, if the host organism is unable to or cannot be enabled to express the appropriate squalene epoxidase.

Examples of nucleic acids encoding a squalene epoxidase are nucleic acids encoding a squalene epoxidase of Saccharomyces cerevisiae (Jandrositz, A., et al (1991) The gene encoding squalene epoxidase from Saccharomyces cerevisiae: cloning and characterization. Gene 107:155-160, of Mus musculus (Kosuga K, Hata S, Osumi T, Sakakibara J, Ono T. (1995) Nucleotide sequence of a cDNA for mouse squalene epoxidase, Biochim Biophys Acta, February 21; 1260(3):345-8b), of Rattus norvegicus (Sakakibara J, Watanabe R, Kanai Y, Ono T. (1995) Molecular cloning and expression of rat squalene epoxidase. J Biol Chem January 6; 270(1):17-20c) or of Homo sapiens (Nakamura Y, Sakakibara J, Izumi T, Shibata A, Ono T. (1996) Transcriptional regulation of squalene epoxidase by sterols and inhibitors in HeLa cells., J. Biol. Chem. 1996, Apr. 5; 271(14):8053-6).

In this preferred embodiment, thus at least one further squalene epoxidase is present in the transgenic organisms of the invention, compared to the wild type.

The number of squalene-epoxidase genes in the transgenic organisms of the invention is at least two, preferably more than two, particularly preferably more than three and very particularly preferably more than five.

Preference is given to using in the above-described method nucleic acids which encode proteins comprising the amino acid sequence SEQ. ID. NO. 28 or a sequence derived from this sequence by substitution, insertion or deletion of amino acids, which is at least 30%, preferably at least 50%, more preferably at least 70%, still more preferably at least 90%, most preferably at least 95%, identical at the amino acid level with the sequence SEQ. ID. NO. 28, and having the enzyme property of a squalene epoxidase.

The sequence SEQ. ID. NO. 28 represents the amino acid sequence of Saccharomyces cerevisiae squalene epoxidase.

Further examples of squalene epoxidases and squalene-epoxidase genes can readily be found, for example, for various organisms whose genomic sequence is known by comparing the homology of the amino acid sequences or the corresponding backtranslated nucleic acid sequences from databases with the SeQ ID. NO. 28.

Further examples of squalene epoxidases and squalene-epoxidase genes can furthermore readily be found for various organisms whose genomic sequence is unknown, for example starting from the sequence SEQ. ID. No. 27, by hybridization techniques and PCR techniques in a manner known per se.

In another preferred embodiment, nucleic acids are introduced into organisms, which encode proteins comprising the amino acid sequence of Saccharomyces cerevisiae squalene epoxidase (SEQ. ID. NO. 28).

Suitable nucleic acid sequences can be obtained, for example, by backtranslating the polypeptide sequence according to the genetic code.

Preference is given to using for this those codons which are frequently used according to the organism-specific codon usage. Said codon usage can readily be determined on the basis of computer analyses of other known genes of the organisms in question.

If the protein is to be expressed in yeast, for example, it is often advantageous to use the codon usage of yeast for backtranslation.

In a particularly preferred embodiment, a nucleic acid comprising the sequence SEQ. ID. NO. 27 is introduced into the organism.

The sequence SEQ. ID. NO. 27 represents the genomic DNA of Saccharomyces cerevisiae (ORF YGR175C), which encodes the squalene epoxidase of the sequence SEQ ID NO. 28.

Furthermore, all of the squalene-epoxidase genes mentioned above can be prepared in a manner known per se by chemical synthesis from the nucleotide building blocks, for example by fragment condensation of individual overlapping complementary nucleic acid building blocks of the double helix. The chemical synthesis of oligonucleotides may be carried out, for example, in a known manner according to the phosphoramidite method (Voet, Voet, 2nd edition, Wiley Press New York, pages 896-897). Annealing of synthetic oligonucleotides and filling-in of gaps with the aid of the Klenow fragment of DNA polymerase and the ligation reactions and also general cloning methods are described in Sambrook et al. (1989), Molecular cloning: A laboratory manual, Cold Spring Harbor Laboratory Press.

In a preferred embodiment, the squalene-synthetase activity is increased compared to the wild type by increasing the gene expression of a nucleic acid encoding a squalene synthetase.

In a further preferred embodiment, gene expression of a nucleic acid encoding a squalene synthetase is increased by introducing into the organism one or more nucleic acids encoding a squalene synthetase.

For this purpose, it is possible to use in principle any squalene-synthetase gene (ERG9), i.e. any nucleic acids encoding a squalene synthetase. In the case of genomic squalene synthetase nucleic acid sequences from eukaryotic sources, which contain introns, already processed nucleic acid sequences such as the corresponding cDNAs are to be used preferably, if the host organism is unable to or cannot be enabled to express the appropriate squalene synthetase.

Examples of nucleic acids encoding a squalene synthetase are nucleic acids encoding a Saccharomyces cerevisiae squalene synthetase (ERG9) (Jennings, S. M., (1991): Molecular cloning and characterization of the yeast gene for squalene synthetase. Proc Natl Acad Sci USA. July 15; 88(14):6038-42), nucleic acids encoding a Botryococcus braunii Okada squalene synthetase (Devarenne, T. P. et al.: Molecular characterization of squalene synthetase from the green microalga Botryococcus braunii, raceB, Arch. Biochem. Biophys. 2000, Jan. 15, 373(2):307-17), nucleic acids encoding a Potato tuber squalene synthetase (Yoshioka H. et al.: cDNA cloning of sesquiter penecyclase and squalene synthase, and expression of the genes in potato tuber infected with Phytophthora infestans, Plant. Cell. Physiol. 1999, September; 40(9):993-8) and nucleic acids encoding a Glycyrrhiza glabra squalene synthetase (Hayashi, H. et al.: Molecular cloning and characterization of two cDNAs for Glycyrrhiza glabra squalene synthase, Biol. Pharm. Bull. 1999, September; 22(9):947-50).

In this preferred embodiment, thus at least one further squalene-synthetase gene is present in the transgenic organisms of the invention, compared to the wild type.

The number of squalene-synthetase genes in the transgenic organisms of the invention is at least two, preferably more than two, particularly preferably more than three and very particularly preferably more than five.

Preference is given to using in the above-described method nucleic acids which encode proteins comprising the amino acid sequence SEQ. ID. NO. 30 or a sequence derived from this sequence by substitution, insertion or deletion of amino acids, which is at least 30%, preferably at least 50%, more preferably at least 70%, still more preferably at least 90%, most preferably at least 95%, identical at the amino acid level with the sequence SEQ. ID. NO. 30, and having the enzyme property of a squalene synthetase.

The sequence SEQ. ID. NO. 30 represents the amino acid sequence of Saccharomyces cerevisiae squalene synthetase (ERG9).

Further examples of squalene synthetases and squalene-synthetase genes can readily be found, for example, for various organisms hose genomic sequence is known by comparing the homology of the amino acid sequences or the corresponding backtranslated nucleic acid sequences from databases with the SeQ ID. NO. 30.

Further examples of squalene synthetases and squalene-synthetase genes can furthermore readily be found for various organisms whose genomic sequence is unknown, for example starting from the sequence SEQ. ID. No. 29, by hybridization techniques and PCR techniques in a manner known per se.

In another preferred embodiment, nucleic acids are introduced into organisms, which encode proteins comprising the amino acid sequence of Saccharomyces cerevisiae squalene synthetase (SEQ. ID. NO. 30).

Suitable nucleic acid sequences can be obtained, for example, by backtranslating the polypeptide sequence according to the genetic code.

Preference is given to using for this those codons which are frequently used according to the organism-specific codon usage. Said codon usage can readily be determined on the basis of computer analyses of other known genes of the organisms in question.

If the protein is to be expressed in yeast, for example, it is often advantageous to use the codon usage of yeast for the backtranslation.

In a particularly preferred embodiment, a nucleic acid comprising the sequence SEQ. ID. NO. 29 is introduced into the organism.

The sequence SEQ. ID. NO. 29 represents the genomic DNA of Saccharomyces cerevisiae (ORF YHR190W), which encodes the squalene synthetase of the sequence SEQ ID NO. 30.

Furthermore, all of the squalene-synthetase genes mentioned above can be prepared in a manner known per se by chemical synthesis from the nucleotide building blocks, for example by fragment condensation of individual overlapping complementary nucleic acid building blocks of the double helix. The chemical synthesis of oligonucleotides may be carried out, for example, in a known manner according to the phosphoramidite method (Voet, Voet, 2nd edition, Wiley Press New York, pages 896-897). Annealing of synthetic oligonucleotides and filling-in of gaps with the aid of the Klenow fragment of DNA polymerase and the ligation reactions and also general cloning methods are described in Sambrook et al. (1989), Molecular cloning: A laboratory manual, Cold Spring Harbor Laboratory Press.

In a preferred embodiment, the sterol-acyltransferase activity is increased compared to the wild type by increasing the gene expression of a nucleic acid encoding a sterol acyltransferase.

In a further preferred embodiment, gene expression of a nucleic acid encoding a sterol acyltransferase is increased by introducing into the organism one or more nucleic acids encoding a sterol acyltransferase.

For this purpose, it is possible to use in principle any sterol-acyltransferase gene (SAT1 or SAT2), i.e. any nucleic acids encoding a sterol acyltransferase.

In the case of genomic sterol acyltransferase nucleic acid sequences from eukaryotic sources, which contain introns, already processed nucleic acid sequences such as the corresponding cDNAs are to be used preferably, if the host organism is unable to or cannot be enabled to express the appropriate sterol acyltransferase.

Examples of nucleic acids encoding a sterol acyltransferase are nucleic acids encoding a Saccharomyces cerevisiae sterol acyltransferase (SAT1) or (SAT2) (Yang, H.: Sterol esterification in yeast: a two-gene process. Science. 1996 May 31; 272(5266):1353-6), a further nucleic acid encoding a further Saccharomyces cerevisiae sterol acyltransferase (J. Biol. Chem. 1996, September 27; 271(39):24157-63), nucleic acids encoding a human sterol acyltransferase (Chang, C. C. et al., Molecular cloning and functional expression of human acyl-coenzyme A: cholesterol acyltransferase cDNA in mutant Chinese hamster ovary cells, J. Biol. Chem. 1993, October 5; 268(28):20747-55) and nucleic acids encoding a murine sterol acyltransferase (Uelmen, P. J.: Tissue-specific expression and cholesterol regulation of acylcoenzyme A:cholesterol acyltransferase (ACAT) in mice. Molecular cloning of mouse ACAT cDNA, chromosomal localization, and regulation of ACAT in vivo and in vitro, J. Biol. Chem. 1995 Nov. 3; 270(44):26192-201).

In this preferred embodiment, thus at least one further sterol-acyltransferase gene is present in the transgenic organisms of the invention, compared to the wild type.

The number of sterol-acyltransferase genes in the transgenic organisms of the invention is at least two, preferably more than two, particularly preferably more than three and very particularly preferably more than five.

Preference is given to using in the above-described method nucleic acids which encode proteins comprising the amino acid sequence SEQ. ID. NO. 32 or SEQ ID NO. 50 or a sequence derived from these sequences by substitution, insertion or deletion of amino acids, which is at least 30%, preferably at least 50%, more preferably at least 70%, still more preferably at least 90%, most preferably at least 95%, identical at the amino acid level with the sequence SEQ. ID. NO. 32 or SEQ. ID. NO. 50, and having the enzyme property of a sterol acyltransferase.

The sequence SEQ. ID. NO. 32 represents the amino acid sequence of Saccharomyces cerevisiae sterol acyltransferase SAT1.

The sequence SEQ. ID. NO. 50 represents the amino acid sequence Saccharomyces cerevisiae sterol acyltransferase SAT2.

SAT 1 and SAT2 differ from one another by a different substrate specificity.

Further examples of sterol acyltransferases and sterol-acyltransferase genes can readily be found, for example, for various organisms whose genomic sequence is known by comparing the homology of the amino acid sequences or the corresponding backtranslated nucleic acid sequences from databases with the SeQ ID. NO. 32 or 50.

Further examples of sterol acyltransferase and sterol-acyltransferase genes can furthermore readily be found for various organisms whose genomic sequence is unknown, for example starting from the sequence SEQ. ID. No. 31 or 49, by hybridization techniques and PCR techniques in a manner known per se.

In another preferred embodiment, nucleic acids are introduced into organisms, which encode proteins comprising the amino acid sequence of Saccharomyces cerevisiae sterol acyltransferase SAT1 (SEQ. ID. NO. 32) or Saccharomyces cerevisiae sterol acyltransferase SAT2 (SEQ. ID. NO. 50).

Suitable nucleic acid sequences can be obtained, for example, by backtranslating the polypeptide sequence according to the genetic code.

Preference is given to using for this those codons which are frequently used according to the organism-specific codon usage. Said codon usage can readily be determined on the basis of computer analyses of other known genes of the organisms in question.

If the protein is to be expressed in yeast, for example, it is often advantageous to use the codon usage of yeast for the backtranslation.

In a particularly preferred embodiment, a nucleic acid comprising the sequence SEQ. ID. NO. 31 or 49 is introduced into the organism.

The sequence SEQ. ID. NO. 31 represents the genomic DNA of Saccharomyces cerevisiae (ORF YNR019W), which encodes the sterol acyltransferase SAT1 of the sequence SEQ ID NO. 32.

The sequence SEQ. ID. NO. 49 represents the genomic DNA of Saccharomyces cerevisiae (ORF YCR048W), which encodes the sterol acyltransferase SAT2 of the sequence SEQ ID NO. 50.

Furthermore, all of the sterol-acyltransferase genes mentioned above can be prepared in a manner known per se by chemical synthesis from the nucleotide building blocks, for example by fragment condensation of individual overlapping complementary nucleic acid building blocks of the double helix. The chemical synthesis of oligonucleotides may be carried out, for example, in a known manner according to the phosphoramidite method (Voet, Voet, 2nd edition, Wiley Press New York, pages 896-897). Annealing of synthetic oligonucleotides and filling-in of gaps with the aid of the Klenow fragment of DNA polymerase and the ligation reactions and also general cloning methods are described in Sambrook et al. (1989), Molecular cloning: A laboratory manual, Cold Spring Harbor Laboratory Press.

According to the invention, organisms mean, for example, bacteria, in particular bacteria of the genus Bacillus, Escherichia coli, Lactobacillus spec. or Streptomyces spec.,

for example yeasts, in particular yeasts of the genus Saccharomyces cerecisiae, Pichia pastoris or Klyveromyces spec. for example fungi, in particular fungi of the genus Aspergillus spec., Penicillium spec. or Dictyostelium spec. and also, for example, insect cell lines, which are capable, either as wild type or owing to previous genetic modification, of producing zymosterol and/or the biosynthetic intermediates and/or secondary products thereof.

Particularly preferred organisms are yeasts, in particular those of the species Saccharomyces cerevisiae, in particular the yeast strains Saccharomyces cerevisiae AH22, Saccharomyces cerevisiae GRF, Saccharomyces cerevisiae DBY747 and Saccharomyces cerevisiae BY4741.

In the case of yeasts as organisms or genetically modified organisms, it is possible, as mentioned above, to increase at least one of the activities selected from the group consisting of Δ8-Δ7-isomerase activity, Δ5-desaturase activity and Δ24-reductase activity by overexpressing the corresponding nucleic acids. The overexpression may be carried out both homologously by introducing nucleic acids intrinsic to yeast and heterologously by introducing nucleic acids from other organisms, in particular mammals, or natural or artificial variants derived therefrom into the yeast. Preference is given to using mammalian genes in yeasts, since these genes have a better substrate specificity with respect to 7-dehydrocholesterol.

The Δ8-Δ7-isomerase activity, Δ5-desaturase activity, Δ24-reductase activity, C24-methyltransferase activity, Δ22-desaturase activity, HMG-CoA-reductase activity, lanosterol-C14-demethylase activity, squalene-epoxidase activity, squalene-synthetase activity and sterol-acyltransferase activity of the genetically modified organism of the invention and of the reference organism is determined under the following conditions:

The activity of HMG-CoA reductase is determined as described in Th. Polakowski, Molekularbiologische Beeinflussung des Ergosterolstoffwechsels der Hefe Saccharomyces cerevisiae [influencing the ergosterol metabolism of the yeast Saccharomyces cerevisiae by molecular biological means], Shaker-Verlag, Aachen 1999, ISBN 3-8265-6211-9, beschrieben.

According to this, 10⁹ yeast cells of a 48 h culture are harvested by centrifugation (3500.times.g, 5 min) and washed in 2 ml of buffer I (100 mM potassium phosphate buffer, pH 7.0). The cell pellet is taken up in 500 μl of buffer 1 (cytosolic proteins) or 2 (100 mM potassium phosphate buffer pH 7.0; 1% Triton X-100) (total proteins), and 1 μl of 500 mM PMSF in isopropanol is added. 500 μl of glass beads (d=0.5 mm) are added to the cells and the cells are disrupted by vortexing 5.times. for one minute each. The liquid between the glass beads is transferred to a new Eppendorf vessel. Cell debris and membrane components are removed by centrifugation (14000.times.g; 15 min). The supernatant is transferred to a new Eppendorf vessel and represents the protein fraction.

The activity of HMG-CoA reductase is determined by measuring NADPH+H⁺ consumption during the reduction of 3-hydroxy-3-methylglutaryl-CoA which is added as substrate.

In a 1000 μl assay mixture, 20 μl of yeast protein isolate are combined with 910 μl of buffer I; 50 μl of 0.1 M DTT and 10 μl of 16 mM NADPH+H⁺. The mixture is adjusted to 30.degree. C. and measured in a spectrophotometer at 340 nm for 7.5 min. The decrease in NADPH, which is measured over this period, is the rate of degradation without addition of substrate and is taken into account as background.

Subsequently, substrate (10 μl of 30 mM HMG-CoA) is added, and measurement continues for another 7.5 min. The HMG-CoA-reductase activity is calculated by determining the specific rate of NADPH degradation.

The activity of lanosterol C14-demethylase is determined as described in Omura, T. and Sato, R. (1964) The carbon monoxide binding pigment in liver microsomes. J. Biol. Chem. 239, 2370-2378. In this assay, the amount of P450 enzyme as holoenzyme with bound heme can be semi-quantified. The (active) holoenzyme (with heme) can be reduced by CO and only the CO-reduced enzyme has an absorption maximum at 450 nm. Thus the absorption maximum at 450 nm is a measure for lanosterol C14-demethylase activity.

The activity is determined by diluting a microsomal fraction (4-10 mg/ml protein in 100 mM potassium phosphate buffer) 1:4 so that the protein concentration used in the assay is 2 mg/ml. The assay is carried out directly in a cuvette.

A spatula tipful of dithionite (S₂O₄Na₂) is added to the microsomes. The baseline is recorded in the 380-500 nm region in a spectrophotometer.

Subsequently, approx. 20-30 CO bubbles are passed through the sample. The absorption is then measured in the same region. The absorption level at 450 nm corresponds to the amount of P450 enzyme in the assay mixture.

The activity of squalene epoxidase is determined as described in Leber R, Landl K, Zinser E, Ahorn H, Spok A, Kohlwein S D, Turnowsky F, Daum G. (1998) Dual localization of squalene epoxidase, Erg1p, in yeast reflects a relationship between the endoplasmic reticulum and lipid particles, Mol. Biol. Cell. 1998, February; 9(2):375-86.

In this method, a total volume of 500 μl contains from 0.35 to 0.7 mg of microsomal protein or from 3.5 to 75 μg of lipid-particle protein in 100 mM Tris-HCl, pH 7.5, 1 mM EDTA, 0.1 mM FAD, 3 mM NADPH, 0.1 mM squalene 2,3-epoxidase cyclase inhibitor U18666A, 32 μM [^(3H)]squalene dispersed in 0.005% Tween 80.

The assay is carried out at 30.degree. C. After 10 minutes of pretreatment, the reaction is started by adding squalene and stopped after 15, 30 or 45 min by lipid extraction with 3 ml of chloroform/methanol (2:1 vol/vol) and 750 μl of 0.035% MgCl₂.

The lipids are dried under nitrogen and redissolved in 0.5 ml of chloroform/methanol (2:1 vol/vol). For thin layer chromatography, portions are applied to a Silica Gel 60 plate (0.2 mm) and fractionated using chloroform as eluent. The positions containing [³]2,3-oxidosqualene and [^(3H)]squalene were scraped off and quantified in a scintillation counter.

The Δ8-Δ7-isomerase activity is determined, with a slight modification, as described in Silve S. et al.: Emopamil-binding Protein, a Mammalian Protein That Binds a Series of Structurally Diverse Neuroprotective Agents, Exhibits 8-7 Sterol Isomerase Activity in Yeast. J Biol Chem 1996 Sep. 13; 271(37):22434-40:

Microsomes prepared from a culture volume of 10 ml are incubated in the presence of 75 μM cholesta-8-en-3-ol at 30.degree. C. for 3 h. The sterols are then extracted with 4 times 5 ml of hexane and purified. Aliquots are analyzed by means of GC/MS.

The Δ5-desaturase activity is determined, with slight modification, as described in Nishi, S. et al. (2000): cDNA cloning of the mammalian sterol C5-desaturase and the expression in yeast mutant. Biochim. Biophys. Acta1490(1-2), 106-108:

Microsomes prepared from a culture volume of 10 ml are incubated in the presence of 75 μM lathosterol and 2 mM NADH at 30.degree. C. for 3 h. The sterols are then extracted with 4 times 5 ml of hexane and purified. Aliquots are analyzed by means of GC/MS.

The Δ24-reductase activity can be determined as described below:

Microsomes prepared from a culture volume of 10 ml are incubated in the presence of 75 μM cholesta-5,7,24-trienol at 30.degree. C. for 3 h. The sterols are then extracted with 4 times 5 ml of hexane and purified. Aliquots are analyzed by means of GC/MS.

The C24-methyltransferase activity can be determined as described below:

80% of the protein Erg6p (C24-methyltransferase) are detectable in lipid particles in the yeast (Athenstaedt K, Zweytick D, Jandrositz A, Kohlwein S D, Daum G: Identification and characterization of major lipid particle proteins of the yeast Saccharomyces cerevisiae. J. Bacteriol. 1999 October; 181(20):6441-8). The enzyme activity is determined by preparing lipid particles from a culture volume (48 h) of 100 ml (according to a method described in Athenstaedt K, Zweytick D, Jandrositz A, Kohlwein S D, Daum G: Identification and characterization of major lipid particle proteins of the yeast Saccharomyces cerevisiae. J. Bacteriol. 1999 October; 181(20):6441-8).

The protein content is determined by a Biorad enzyme assay and 3 mg of protein are used in a volume of 500 μl for each assay mixture. 50 μM [methyl-³H₃]-S-adenosylmethionine and 50 μM zymosterol are added to the assay mixture which is then incubated at 35.degree. C. for 10 min. Subsequently, the same volume (500 μl) of chloroform/methanol (4:1) is added and the sterols are then extracted.

The proportion of zymosterol with incorporated [methyl-³H₃]-S-adenosylmethionine can be determined by means of scintillation measurement, since chloroform/methanol extraction extracts only lipid-soluble substances. For quantification, the radioactive decays are likewise determined for 50 μM [methyl-³H₃]-S-adenosylmethionine by means of scintillation measurement.

This method is a modification of the method described in Nes W D, Guo D, Zhou W.: Substrate-based inhibitors of the (S)-adenosyl-L-methionine:Δ24(25)- to Δ24(28)-sterol methyl transferase from Saccharomyces cerevisiae, Arch. Biochem. Biophys. 1997 Jun. 1; 342(1):68-81.

The activity of Δ22-desaturase (ERG5p) can be determined as described below:

Various concentrations of Ergosta-5,7-dienol, purified from S. cerevisiae erg5 mutants (Parks et al, 1985. Yeast sterols. yeast mutants as tools for the study of sterol metabolism. Methods Enzymol. 111:333-346) and 50 μg of dilauroylphosphatidylcholine are mixed and treated with ultrasound until a white suspension is formed. Prepared microsomes are added (1 ml) (3 mg/ml protein). NADPH (1 mM final concentration) is added to the assay mixture to start the enzyme reaction. The mixture is incubated at 37.degree. C. for 20 min. The reaction is stopped by adding 3 ml of methanol and sterols are hydrolyzed by adding 2 ml of 60% (wt/vol) KOH in water. The mixture is incubated at 90.degree. C. for 2 h. After cooling, the mixture is extracted three times with 5 ml of hexane and concentrated in a rotary evaporator. Subsequently, the sterols are silylated with bis(trimethylsilyl)trifluoroacetamide (50 μl in 50 μl toluene) at 60.degree. C. for 1 h. The sterols are analyzed by gas chromatography-mass spectrometry (GC-MS) (for example Model VG 12-250 gas chromatograph-mass spectrometer; VG Biotech, Manchester, United Kingdom). The resultant Δ22-desaturated intermediate can be identified depending on the amount of substrate used. Microsomes which are not incubated with substrate serve as reference.

This method is a modification of the method described in Lamb et al: Purification, reconstitution, and inhibition of cytochrome P-450 sterol Δ22-desaturase from the pathogenic fungus Candida glabrata. Antimicrob Agents Chemother. 1999 July; 43(7):1725-8.

The squalene-synthetase activity can be determined as described below:

The assays contain 50 mM MOPS, pH 7.2, 10 mM MgCl₂, 1% (v/v) Tween-80, 10% (v/v) 2-propanol, 1 mM DTT, 1 mg/mL BSA, NADPH, FPP (or PSPP) and microsomes (protein content 3 mg) in a total volume of 200 μl in glass tubes. The reaction mixtures containing the radioactive substrate [1-³H]FPP (15-30 mCi/μmol) are incubated at 30.degree. C. for 30 min and one volume of 1:1 (v/v) 40% aqueous KOH:methanol is added to the suspension mixture. Liquid NaCl is added to saturate the solution and 2 ml of naphtha containing 0.5% (v/v) squalene are likewise added.

The suspension is vortexed for 30 s. In each case 1 ml of the naphtha layer is applied to a packed 0.5.times.6 cm aluminum column (80-200 mesh, Fisher) using a Pasteur pipette. The column has been pre-equilibrated with 2 ml of naphtha containing 0.5% (v/v) squalene. The column is then eluted with 5.times.1 ml of toluene containing 0.5% (v/v) squalene. Squalene radioactivity is measured in Cytoscint (ICN) scintillation cocktail in a scintillation counter (Beckman).

This method is a modification of the method described in Radisky et al., Biochemistry. 2000 Feb. 22; 39(7):1748-60, Zhang et al. (1993) Arch. Biochem. Biophys. 304, 133-143 and Poulter, C. D. et al. (1989) J. Am. Chem. Soc. 111, 3734-3739.

The sterol-acyltransferase activity can be determined as described below:

A 200 ml main culture is inoculated at 1% strength from a 20 ml preculture which has been incubated for two days and is incubated in complete medium overnight. The cells are harvested and then washed in two volumes of HP buffer (100 mM potassium phosphate buffer, pH 7.4; 0.5 mM EDTA; 1 mM glutathione; 20 μM leupeptin; 64 μM benzamidine; 2 mM PMSF) and resuspended in HP buffer.

After adding 1 g of glass beads, the cells are disrupted by vortexing 8 times for one minute each. The supernatant is ultracentrifuged at 105000.times.g. The pellet is taken up in 1 ml of ACAT buffer (100 mM potassium phosphate buffer pH7.4; 1 mM glutathione).

The enzyme assay is carried out in a volume of 500 μl. The substrate ergosterol is taken up in 62.5 ml of 0.5.times. ACAT buffer with vigorous vortexing. 250 μl of this solution are used as substrate in the assay. To this, 20 μl of protein extract, 50 μl of water and 130 μl of 0.5.times. ACAT buffer are added.

The mixture is incubated at 37.degree. C. for 15 min. Subsequently, 50 μl of 14C-oleoyl-CoA (600000 dpm) are added and the reaction is stopped after one minute by adding 4 ml of chloroform/methanol (2:1). To this, 500 μl of H₂O are added. The phases are separated by briefly centrifuging the suspension at 2000.times.g. The lower phase is evaporated to dryness in a pear-shaped flask and redissolved in 100 μl of chloroform/methanol (4:1) and applied to a TLC plate (silica gel 60 F254). The TLC is carried out using petroleum ether/diethyl ether/acetic acid 90:10:1 as eluent. The spots of the steryl ester fractions are cut out and the number of radioactive decays is determined in a scintillation column. The enzyme activity can be determined via the amount of sterile ester-bound 14C-oleoyl-CoA molecules.

In a preferred embodiment of the method of the invention 7-dehydrocholesterol and/or the biosynthetic intermediates and/or intermediates thereof are prepared by culturing organisms, in particular yeasts, which have, compared to the wild type, an increased activity of at least one of the activities selected from the group consisting of Δ8-Δ7-isomerase activity, Δ5-desaturase activity and Δ24-reductase activity and which have additionally a reduced activity of at least one of the activities selected from the group consisting of C24-methyltransferase activity and Δ22-desaturase activity and which have additionally an increased HMG-CoA-reductase activity, an increased lanosterol-C14-demethylase activity and an increased squalene-epoxidase activity.

In other preferred embodiments of the method of the invention, 7-dehydrocholesterol and/or the biosynthetic intermediates and/or secondary products thereof are prepared by culturing organisms, in particular yeasts, which have, compared to the wild type,

an increased Δ8-Δ7-isomerase activity, an increased Δ5-desaturase activity, an increased Δ24-reductase activity, an increased Δ8-Δ7-isomerase activity and an increased Δ5-desaturase activity, an increased Δ8-Δ7-isomerase activity and an increased Δ24-reductase activity, an increased Δ5-desaturase activity and an increased Δ24-reductase activity, an increased Δ8-Δ7-isomerase activity, an increased Δ5-desaturase activity and an increased Δ24-reductase activity, an increased Δ8-Δ7-isomerase activity and a reduced C24-methyltransferase activity, an increased Δ5-desaturase activity and a reduced C24-methyltransferase activity, an increased Δ24-reductase activity and a reduced C24-methyltransferase activity, an increased Δ8-Δ7-isomerase activity, an increased Δ5-desaturase activity and a reduced C24-methyltransferase activity, an increased Δ8-Δ7-isomerase activity, an increased Δ24-reductase activity and a reduced C24-methyltransferase activity, an increased Δ5-desaturase activity, an increased Δ24-reductase activity and a reduced C24-methyltransferase activity, an increased Δ8-Δ7-isomerase activity, an increased Δ5-desaturase activity, an increased Δ24-reductase activity and a reduced C24-methyltransferase activity, an increased Δ8-Δ7-isomerase activity and a reduced Δ22-desaturase activity, an increased Δ5-desaturase activity and a reduced Δ22-desaturase activity, an increased Δ24-reductase activity and a reduced Δ22-desaturase activity, an increased Δ8-Δ7-isomerase activity, an increased Δ5-desaturase activity and a reduced Δ22-desaturase activity, an increased Δ8-Δ7-isomerase activity, an increased Δ24-reductase activity and a reduced Δ22-desaturase activity, an increased Δ5-desaturase activity, an increased Δ24-reductase activity and a reduced Δ22-desaturase activity, an increased Δ8-Δ7-isomerase activity, an increased Δ5-desaturase activity, an increased Δ24-reductase activity and a reduced Δ22-desaturase activity, an increased Δ8-Δ7-isomerase activity, a reduced Δ22-desaturase activity and a reduced C24-ethyltransferase activity, an increased Δ5-desaturase activity, a reduced Δ22-desaturase activity and a reduced C24-methyltransferase activity, an increased Δ24-reductase activity, a reduced Δ22-desaturase activity and a reduced C24-methyltransferase activity, an increased Δ8-Δ7-isomerase activity, an increased Δ5-desaturase activity, a reduced Δ22-desaturase activity and a reduced C24-methyltransferase activity, an increased Δ8-Δ7-isomerase activity, an increased Δ24-reductase activity, a reduced Δ22-desaturase activity and a reduced C24-methyltransferase activity, an increased Δ5-desaturase activity, an increased Δ24-reductase activity, a reduced Δ22-desaturase activity and a reduced C24-methyltransferase activity, an increased Δ8-Δ7-isomerase activity, an increased Δ5-desaturase activity, an increased Δ24-reductase activity, a reduced Δ22-desaturase activity and a reduced C24-methyltransferase activity, an increased Δ8-Δ7-isomerase activity and an increased HMG-CoA-reductase activity, an increased Δ5-desaturase activity and an increased HMG-CoA-reductase activity, an increased Δ24-reductase activity and an increased HMG-CoA-reductase activity, an increased Δ8-Δ7-isomerase activity, an increased HMG-CoA-reductase activity and an increased Δ5-desaturase activity, an increased Δ8-Δ7-isomerase activity, an increased HMG-CoA-reductase activity and an increased Δ24-reductase activity, an increased Δ5-desaturase activity, an increased HMG-CoA-reductase activity and an increased Δ24-reductase activity, an increased Δ8-Δ7-isomerase activity, an increased Δ5-desaturase activity, an increased HMG-CoA-reductase activity and an increased Δ24-reductase activity, an increased Δ8-Δ7-isomerase activity, an increased HMG-CoA-reductase activity and a reduced C24-methyltransferase activity, an increased Δ5-desaturase activity, an increased HMG-CoA-reductase activity and a reduced C24-methyltransferase activity, an increased Δ24-reductase activity, an increased HMG-CoA-reductase activity and a reduced C24-methyltransferase activity, an increased Δ8-Δ7-isomerase activity, an increased Δ5-desaturase activity, an increased HMG-CoA-reductase activity and a reduced C24-methyltransferase activity, an increased Δ8-Δ7-isomerase activity, an increased Δ24-reductase activity, an increased HMG-CoA-reductase activity and a reduced C24-methyltransferase activity, an increased Δ5-desaturase activity, an increased Δ24-reductase activity and a reduced C24-methyltransferase activity, an increased Δ8-Δ7-isomerase activity, an increased Δ5-desaturase activity, an increased Δ24-reductase activity, an increased HMG-CoA-reductase activity and a reduced C24-methyltransferase activity, an increased Δ8-Δ7-isomerase activity, an increased HMG-CoA-reductase activity and a reduced Δ22-desaturase activity, an increased Δ5-desaturase activity, an increased HMG-CoA-reductase activity and a reduced Δ22-desaturase activity, an increased Δ24-reductase activity, an increased HMG-CoA-reductase activity and a reduced Δ22-desaturase activity, an increased Δ8-Δ7-isomerase activity, an increased Δ5-desaturase activity, an increased HMG-CoA-reductase activity and a reduced Δ22-desaturase activity, an increased Δ8-Δ7-isomerase activity, an increased Δ24-reductase activity, an increased HMG-CoA-reductase activity and a reduced Δ22-desaturase activity, an increased Δ5-desaturase activity, an increased Δ24-reductase activity, an increased HMG-CoA-reductase activity and a reduced Δ22-desaturase activity, an increased Δ8-Δ7-isomerase activity, an increased Δ5-desaturase activity, an increased Δ24-reductase activity, an increased HMG-CoA-reductase activity and a reduced Δ22-desaturase activity, an increased Δ8-Δ7-isomerase activity, a reduced Δ22-desaturase activity, an increased HMG-CoA-reductase activity and a reduced C24-methyltransferase activity, an increased Δ5-desaturase activity, a reduced Δ22-desaturase activity, an increased HMG-CoA-reductase activity and a reduced C24-methyltransferase activity, an increased Δ24-reductase activity, a reduced Δ22-desaturase activity, an increased HMG-CoA-reductase activity and a reduced C24-methyltransferase activity, an increased Δ8-Δ7-isomerase activity, an increased Δ5-desaturase activity, a reduced Δ22-desaturase activity, an increased HMG-CoA-reductase activity and a reduced C24-methyltransferase activity, an increased Δ8-Δ7-isomerase activity, an increased Δ24-reductase activity, a reduced Δ22-desaturase activity, an increased HMG-CoA-reductase activity and a reduced C24-methyltransferase activity, an increased Δ5-desaturase activity, an increased Δ24-reductase activity, a reduced Δ22-desaturase activity, an increased HMG-CoA-reductase activity and a reduced C24-methyltransferase activity, an increased Δ8-Δ7-isomerase activity, an increased Δ5-desaturase activity, an increased Δ24-reductase activity, a reduced Δ22-desaturase activity, an increased HMG-CoA-reductase activity and a reduced C24-methyltransferase activity, an increased Δ8-Δ7-isomerase activity and an increased lanosterol-C14-demethylase activity, an increased Δ5-desaturase activity and an increased lanosterol-C14-demethylase activity, an increased Δ24-reductase activity and an increased lanosterol-C14-demethylase activity, an increased Δ8-Δ7-isomerase activity, an increased lanosterol-C14-demethylase activity and an increased Δ5-desaturase activity, an increased Δ8-Δ7-isomerase activity, an increased lanosterol-C14-demethylase activity and an increased Δ24-reductase activity, an increased Δ5-desaturase activity, an increased lanosterol-C14-demethylase activity and an increased Δ24-reductase activity, an increased Δ8-Δ7-isomerase activity, an increased Δ5-desaturase activity, an increased lanosterol-C14-demethylase activity and an increased Δ24-reductase activity, an increased Δ8-Δ7-isomerase activity, an increased lanosterol-C14-demethylase activity and a reduced C24-methyltransferase activity, an increased Δ5-desaturase activity and a reduced C24-methyltransferase activity, an increased Δ24-reductase activity, an increased lanosterol-C14-demethylase activity and a reduced C24-methyltransferase activity, an increased Δ8-Δ7-isomerase activity, an increased Δ5-desaturase activity, an increased lanosterol-C14-demethylase activity and a reduced C24-methyltransferase activity, an increased Δ8-Δ7-isomerase activity, an increased Δ24-reductase activity, an increased lanosterol-C14-demethylase activity and a reduced C24-methyltransferase activity, an increased Δ5-desaturase activity, an increased Δ24-reductase activity, an increased lanosterol-C14-demethylase activity and a reduced C24-methyltransferase activity, an increased Δ8-Δ7-isomerase activity, an increased Δ5-desaturase activity, an increased Δ24-reductase activity, an increased lanosterol-C14-demethylase activity and a reduced C24-methyltransferase activity, an increased Δ8-Δ7-isomerase activity, an increased lanosterol-C14-demethylase activity and a reduced Δ22-desaturase activity, an increased Δ5-desaturase activity, an increased lanosterol-C14-demethylase activity and a reduced Δ22-desaturase activity, an increased Δ24-reductase activity, an increased lanosterol-C14-demethylase activity and a reduced Δ22-desaturase activity, an increased Δ8-Δ7-isomerase activity, an increased Δ5-desaturase activity, an increased lanosterol-C14-demethylase activity and a reduced Δ22-desaturase activity, an increased Δ8-Δ7-isomerase activity, an increased Δ24-reductase activity, an increased lanosterol-C14-demethylase activity and a reduced Δ22-desaturase activity, an increased Δ5-desaturase activity, an increased Δ24-reductase activity, an increased lanosterol-C14-demethylase activity and a reduced Δ22-desaturase activity, an increased Δ8-Δ7-isomerase activity, an increased Δ5-desaturase activity, an increased Δ24-reductase activity, an increased lanosterol-C14-demethylase activity and a reduced Δ22-desaturase activity, an increased Δ8-Δ7-isomerase activity, a reduced Δ22-desaturase activity, an increased lanosterol-C14-demethylase activity and a reduced C24-methyltransferase activity, an increased Δ5-desaturase activity, a reduced Δ22-desaturase activity, an increased lanosterol-C14-demethylase activity and a reduced C24-methyltransferase activity, an increased Δ24-reductase activity, a reduced Δ22-desaturase activity, an increased lanosterol-C14-demethylase activity and a reduced C24-methyltransferase activity, an increased Δ8-Δ7-isomerase activity, an increased Δ5-desaturase activity, a reduced Δ22-desaturase activity, an increased lanosterol-C14-demethylase activity and a reduced C24-methyltransferase activity, an increased Δ8-Δ7-isomerase activity, an increased Δ24-reductase activity, a reduced Δ22-desaturase activity, an increased lanosterol-C14-demethylase activity and a reduced C24-methyltransferase activity, an increased Δ5-desaturase activity, an increased Δ24-reductase activity, a reduced Δ22-desaturase activity, an increased lanosterol-C14-demethylase activity and a reduced C24-methyltransferase activity, an increased Δ8-Δ7-isomerase activity, an increased Δ5-desaturase activity, an increased Δ24-reductase activity, a reduced Δ22-desaturase activity, an increased lanosterol-C14-demethylase activity and a reduced C24-methyltransferase activity, an increased Δ8-Δ7-isomerase activity, an increased lanosterol-C14-demethylase activity and an increased HMG-CoA-reductase activity, an increased Δ5-desaturase activity, an increased lanosterol-C14-demethylase activity and an increased HMG-CoA-reductase activity, an increased Δ24-reductase activity, an increased lanosterol-C14-demethylase activity and an increased HMG-CoA-reductase activity, an increased Δ8-Δ7-isomerase activity, an increased HMG-CoA-reductase activity, an increased lanosterol-C14-demethylase activity and an increased Δ5-desaturase activity, an increased Δ8-Δ7-isomerase activity, an increased HMG-CoA-reductase activity, an increased lanosterol-C14-demethylase activity and an increased Δ24-reductase activity, an increased Δ5-desaturase activity, an increased HMG-CoA-reductase activity, an increased lanosterol-C14-demethylase activity and an increased Δ24-reductase activity, an increased Δ8-Δ7-isomerase activity, an increased Δ5-desaturase activity, an increased HMG-CoA-reductase activity, an increased lanosterol-C14-demethylase activity and an increased Δ24-reductase activity, an increased Δ8-Δ7-isomerase activity, an increased HMG-CoA-reductase activity, an increased lanosterol-C14-demethylase activity and a reduced C24-methyltransferase activity, an increased Δ5-desaturase activity, an increased HMG-CoA-reductase activity, an increased lanosterol-C14-demethylase activity and a reduced C24-methyltransferase activity, an increased Δ24-reductase activity, an increased HMG-CoA-reductase activity, an increased lanosterol-C14-demethylase activity and a reduced C24-methyltransferase activity, an increased Δ8-Δ7-isomerase activity, an increased Δ5-desaturase activity, an increased HMG-CoA-reductase activity, an increased lanosterol-C14-demethylase activity and a reduced C24-methyltransferase activity, an increased Δ8-Δ7-isomerase activity, an increased Δ24-reductase activity, an increased HMG-CoA-reductase activity, an increased lanosterol-C14-demethylase activity and a reduced C24-methyltransferase activity, an increased Δ5-desaturase activity, an increased Δ24-reductase activity, an increased lanosterol-C14-demethylase activity and a reduced C24-methyltransferase activity, an increased Δ8-Δ7-isomerase activity, an increased Δ5-desaturase activity, an increased Δ24-reductase activity, an increased HMG-CoA-reductase activity, an increased lanosterol-C14-demethylase activity and a reduced C24-methyltransferase activity, an increased Δ8-Δ7-isomerase activity, an increased HMG-CoA-reductase activity, an increased lanosterol-C14-demethylase activity and a reduced Δ22-desaturase activity, an increased Δ5-desaturase activity, an increased HMG-CoA-reductase activity, an increased lanosterol-C14-demethylase activity and a reduced Δ22-desaturase activity, an increased Δ24-reductase activity, an increased HMG-CoA-reductase activity, an increased lanosterol-C14-demethylase activity and a reduced Δ22-desaturase activity, an increased Δ8-Δ7-isomerase activity, an increased Δ5-desaturase activity, an increased HMG-CoA-reductase activity, an increased lanosterol-C14-demethylase activity and a reduced Δ22-desaturase activity, an increased Δ8-Δ7-isomerase activity, an increased Δ24-reductase activity, an increased HMG-CoA-reductase activity, an increased lanosterol-C14-demethylase activity and a reduced Δ22-desaturase activity, an increased Δ5-desaturase activity, an increased Δ24-reductase activity, an increased HMG-CoA-reductase activity and a reduced Δ22-desaturase activity, an increased Δ8-Δ7-isomerase activity, an increased Δ5-desaturase activity, an increased Δ24-reductase activity, an increased HMG-CoA-reductase activity, an increased lanosterol-C14-demethylase activity and a reduced Δ22-desaturase activity, an increased Δ8-Δ7-isomerase activity, a reduced Δ22-desaturase activity, an increased HMG-CoA-reductase activity, an increased lanosterol-C14-demethylase activity and a reduced C24-methyltransferase activity, an increased Δ5-desaturase activity, a reduced Δ22-desaturase activity, an increased HMG-CoA-reductase activity, an increased lanosterol-C14-demethylase activity and a reduced C24-methyltransferase activity, an increased Δ24-reductase activity, a reduced Δ22-desaturase activity, an increased HMG-CoA-reductase activity, an increased lanosterol-C14-demethylase activity and a reduced C24-methyltransferase activity, an increased Δ8-Δ7-isomerase activity, an increased Δ5-desaturase activity, a reduced Δ22-desaturase activity, an increased HMG-CoA-reductase activity, an increased lanosterol-C14-demethylase activity and a reduced C24-methyltransferase activity, an increased Δ8-Δ7-isomerase activity, an increased Δ24-reductase activity, a reduced Δ22-desaturase activity, an increased HMG-CoA-reductase activity, an increased lanosterol-C14-demethylase activity and a reduced C24-methyltransferase activity, an increased Δ5-desaturase activity, an increased Δ24-reductase activity, a reduced Δ22-desaturase activity, an increased HMG-CoA-reductase activity, an increased lanosterol-C14-demethylase activity and a reduced C24-methyltransferase activity, an increased Δ8-Δ7-isomerase activity, an increased Δ5-desaturase activity, an increased Δ24-reductase activity, a reduced Δ22-desaturase activity, an increased HMG-CoA-reductase activity, an increased lanosterol-C14-demethylase activity and a reduced C24-methyltransferase activity, an increased Δ8-Δ7-isomerase activity, an increased Δ5-desaturase activity, an increased Δ24-reductase activity, a reduced Δ22-desaturase activity, an increased HMG-CoA-reductase activity, an increased lanosterol-C14-demethylase activity and a reduced C24-methyltransferase activity, an increased Δ8-Δ7-isomerase activity, an increased Δ5-desaturase activity, an increased Δ24-reductase activity, a reduced Δ22-desaturase activity, an increased HMG-CoA-reductase activity, an increased lanosterol-C14-demethylase activity, an increased squalene-epoxidase activity and a reduced C24-methyltransferase activity, or an increased Δ8-Δ7-isomerase activity, an increased Δ5-desaturase activity, an increased Δ24-reductase activity, a reduced Δ22-desaturase activity, an increased HMG-CoA-reductase activity, an increased lanosterol-C14-demethylase activity, an increased squalene-epoxidase activity and a reduced C24-methyltransferase activity.

In further particularly preferred embodiments of the method of the invention, 7-dehydrocholesterol and/or the biosynthetic intermediates and/or secondary products thereof are prepared by culturing organisms, in particular yeasts, which have, compared to the wild type, an increased Δ8-Δ7-isomerase activity, an increased Δ5-desaturase activity, an increased Δ24-reductase activity, a reduced Δ22-desaturase activity, an increased HMG-CoA-reductase activity, an increased lanosterol-C14-demethylase activity and an increased squalene-epoxidase activity,

an increased Δ8-Δ7-isomerase activity, an increased Δ5-desaturase activity, an increased Δ24-reductase activity, an increased HMG-CoA-reductase activity, an increased lanosterol-C14-demethylase activity, an increased squalene-epoxidase activity and a reduced C24-methyltransferase activity, an increased Δ8-Δ7-isomerase activity, an increased Δ5-desaturase activity, an increased Δ24-reductase activity, a reduced Δ22-desaturase activity, an increased HMG-CoA-reductase activity, an increased lanosterol-C14-demethylase activity, an increased squalene-epoxidase activity and a reduced C24-methyltransferase activity, an increased Δ8-Δ7-isomerase activity, an increased Δ5-desaturase activity, an increased Δ24-reductase activity, a reduced Δ22-desaturase activity, an increased HMG-CoA-reductase activity, an increased lanosterol-C14-demethylase activity, an increased squalene-epoxidase activity, an increased squalene-synthetase activity and a reduced C24-methyltransferase activity, an increased Δ8-Δ7-isomerase activity, an increased Δ5-desaturase activity, an increased Δ24-reductase activity, a reduced Δ22-desaturase activity, an increased HMG-CoA-reductase activity, an increased lanosterol-C14-demethylase activity, an increased squalene-epoxidase activity, an increased sterol-acyltransferase activity and a reduced C24-methyltransferase activity, an increased Δ8-Δ7-isomerase activity, an increased Δ5-desaturase activity, an increased Δ24-reductase activity, a reduced Δ22-desaturase activity, an increased HMG-CoA-reductase activity, an increased lanosterol-C14-demethylase activity, an increased squalene-epoxidase activity, an increased squalene-synthetase activity, an increased sterol-acyltransferase activity and a reduced C24-methyltransferase activity.

Biosynthetic 7-dehydrocholesterol intermediates mean all compounds which appear as intermediates during 7-dehydrocholesterol biosynthesis in the organism used, preferably the compounds mevalonate, farnesyl pyrophosphate, geraniol pyrophosphate, squalene epoxide, 4-dimethylcholesta-8,14,24-trienol, 4,4-dimethylzymosterol, squalene, farnesol, geraniol, lanosterol, zymosterol, lathosterol, cholesta-7,24-dienol and cholesta-5,7,24-trienol.

Biosynthetic secondary products of zymosterol mean all compounds which can be derived biosynthetically from 7-dehydrocholesterol in the organism used, i.e. for which 7-dehydrocholesterol appears as an intermediate. These may be compounds which the organism used produces naturally from 7-dehydrocholesterol, such as, for example, cholesterol or vitamin D3 in mammals. However, they also mean compounds which can be produced in the organism from 7-dehydrocholesterol only by introducing genes and enzyme activities of other organisms for which the starting organism has no orthologous gene.

It is possible, for example, to prepare secondary products from 7-dehydrocholesterol, which are naturally present only in mammals, by introducing mammalian genes into yeast:

Introducing a human or murine nucleic acid encoding a human or murine Δ-7-reductase enables the yeast to produce cholesterol.

Under UV irradiation, vitamin D₃ (cholecalciferol) is produced from 7-dehydrocholesterol via provitamin D₃ by rearrangement.

Therefore, the biosynthetic secondary products of 7-dehydrocholesterol mean in particular provitamin D3, vitamin D₃ (cholecalciferol) and/or cholesterol.

Preferred biosynthetic secondary products are provitamin D₃ and in particular vitamin D₃.

The compounds prepared in the method of the invention may be used in biotransformations, chemical reactions and for therapeutic purposes, for example for producing vitamin D₃ from 7-dehydrocholesterol via UV irradiation, or for producing steroid hormones via biotransformation starting from cholesta-7,24-dienol or cholesta-5,7,24-trienol.

In the inventive method for preparing 7-dehydrocholesterol and/or the biosynthetic intermediates and/or secondary products thereof, the step of culturing the genetically modified organisms, also referred to as transgenic organisms hereinbelow, is preferably followed by harvesting said organisms and isolating 7-dehydrocholesterol and/or the biosynthetic intermediates and/or secondary products thereof from said organisms.

The organisms are harvested in a manner known per se and appropriate for the particular organism. Microorganisms such as bacteria, mosses, yeasts and fungi or plant cells which are cultured in liquid media by fermentation may be removed, for example, by centrifugation, decanting or filtration.

7-Dehydrocholesterol and/or the biosynthetic intermediates and/or secondary products thereof are isolated from the harvested biomass together or each compound is harvested separately in a manner known per se, for example by extraction and, where appropriate, further chemical or physical purification processes such as, for example, precipitation methods, crystallography, thermal separation methods such as rectification methods or physical separation methods such as, for example, chromatography.

The transgenic organisms, in particular yeasts, are preferably prepared either by transforming the starting organisms, in particular yeasts, with a nucleic acid construct containing at least one nucleic acid selected from the group consisting of nucleic acids encoding a Δ8-Δ7-isomerase, nucleic acids encoding a Δ5-desaturase and nucleic acids encoding a Δ24-reductase which are functionally linked with one or more regulatory signals ensuring transcription and translation in organisms. In this embodiment, the transgenic organisms are prepared using a nucleic acid construct.

In a particularly preferred embodiment, the above-described nucleic acid construct additionally contains at least one nucleic acid selected from the group consisting of nucleic acids encoding an HMG-CoA-reductase activity, nucleic acids encoding a lanosterol-C14-demethylase, nucleic acids encoding a squalene epoxidase, nucleic acids encoding a squalene synthetase and nucleic acids encoding a sterol acyltransferase which are functionally linked to one or more regulatory signals ensuring transcription and translation in organisms.

However, the transgenic organisms may also preferably be prepared by transforming the starting organisms, in particular yeasts, with at least one nucleic acid construct selected from the group consisting of nucleic acid constructs containing nucleic acids encoding a Δ8-Δ7-isomerase, nucleic acid construct containing nucleic acids encoding a Δ5-desaturase and nucleic acid construct containing nucleic acids encoding a Δ24-reductase which nucleic acids are in each case functionally linked to one or more regulatory signals ensuring transcription and translation in organisms. In this embodiment, the transgenic organisms are prepared using individual nucleic acid constructs or a combination of nucleic acid constructs.

In a particularly preferred embodiment, the above-described combination of nucleic acid constructs additionally comprises at least one nucleic acid construct selected from the group consisting of nucleic acid construct containing nucleic acids encoding an HMG-CoA-reductase activity, nucleic acid construct containing nucleic acids encoding a lanosterol-C14-demethylase, nucleic acid construct containing nucleic acids encoding a squalene epoxidase, nucleic acid construct containing nucleic acids encoding a squalene synthetase and nucleic acid construct containing nucleic acids encoding a sterol acyltransferase which nucleic acids are in each case functionally linked to one or more regulatory signals ensuring transcription and translation in organisms.

Nucleic acid constructs in which the encoding nucleic acid sequence is functionally linked to one or more regulatory signals ensuring transcription and translation in organisms, in particular in yeasts, are also referred to as expression cassettes hereinbelow.

Examples of nucleic acid constructs containing said expression cassette are vectors and plasmids.

Accordingly, the invention further relates to nucleic acid constructs, in particular nucleic acid constructs functioning as expression cassettes, which contain at least one nucleic acid selected from the group consisting of nucleic acids encoding a Δ8-Δ7-isomerase, nucleic acids encoding a Δ5-desaturase and nucleic acids encoding a Δ24-reductase which are functionally linked to one or more regulatory signals ensuring transcription and translation in organisms.

In a preferred embodiment, said nucleic acid construct additionally comprises at least one nucleic acid selected from the group consisting of nucleic acids encoding an HMG-CoA-reductase activity, nucleic acids encoding a lanosterol-C14-demethylase, nucleic acids encoding a squalene epoxidase, nucleic acids encoding a squalene synthetase and nucleic acids encoding a sterol acyltransferase which are functionally linked to one or more regulatory signals ensuring transcription and translation in organisms.

As an alternative, it is also possible to prepare the transgenic organisms of the invention by transformation with individual nucleic acid constructs or with a combination of nucleic acid constructs, said combination comprising at least one nucleic acid construct selected from the groups A to C

A nucleic acid construct comprising nucleic acids encoding a Δ8-Δ7-isomerase, which are functionally linked to one or more regulatory signals ensuring transcription and translation in organisms,

B nucleic acid construct comprising nucleic acids encoding a Δ5-desaturase, which are functionally linked to one or more regulatory signals ensuring transcription and translation in organisms and

C nucleic acid construct comprising nucleic acids encoding a Δ24-reductase, which are functionally linked to one or more regulatory signals ensuring transcription and translation in organisms, and at least one nucleic acid construct selected from the groups D to H

D nucleic acid construct comprising nucleic acids encoding an HMG-CoA reductase, which are functionally linked to one or more regulatory signals ensuring transcription and translation in organisms, E nucleic acid construct comprising nucleic acids encoding a lanosterol C14-demethylase, which are functionally linked to one or more regulatory signals ensuring transcription and translation in organisms, F nucleic acid construct comprising nucleic acids encoding a squalene epoxidase, which are functionally linked to one or more regulatory signals ensuring transcription and translation in organisms, G nucleic acid construct comprising nucleic acids encoding a squalene synthetase, which are functionally linked to one or more regulatory signals ensuring transcription and translation in organisms, H nucleic acid construct comprising nucleic acids encoding a sterol acyltransferase, which are functionally linked to one or more regulatory signals ensuring transcription and translation in organisms.

The regulatory signals preferably contain one or more promoters which ensure transcription and translation in organisms, in particular in yeasts.

The expression cassettes include regulatory signals, i.e. regulatory nucleic acid sequences, which control expression of the coding sequence in the host cell. According to a preferred embodiment, an expression cassette comprises upstream, i.e. at the 5′ end of the coding sequence, a promoter and downstream, i.e. at the 3′ end, a terminator and, where appropriate, further regulatory elements which are operatively linked to the coding sequence for at least one of the above-described genes located in between.

Operative linkage means the sequential arrangement of promoter, coding sequence, where appropriate, terminator and, where appropriate, further regulatory elements in such a way that each of the regulatory elements can properly carry out its function in the expression of the coding sequence.

The preferred nucleic acid constructs, expression cassettes and plasmids for yeasts and fungi and methods for preparing transgenic yeasts and also the transgenic yeasts themselves are described by way of example below.

A suitable promoter of the expression cassette is in principle any promoter which is able to control the expression of foreign genes in organisms, in particular in yeasts.

Preference is given to using in particular a promoter which is subject to reduced regulation in yeast, such as, for example, the medium ADH promoter.

This promoter fragment of the ADH12s promoter, also referred to as ADH1 hereinbelow, exhibits nearly constitutive expression (Ruohonen L, Penttila M, Keranen S. (1991) Optimization of Bacillus α-amylase production by Saccharomyces cerevisiae. Yeast. May-June; 7(4):337-462; Lang C, Looman A C. (1995) Efficient expression and secretion of Aspergillus niger RH5344 polygalacturonase in Saccharomyces cerevisiae. Appl Microbiol Biotechnol. December; 44(1-2):147-56) so that transcriptional regulation no longer proceeds via intermediates of ergosterol biosynthesis.

Other preferred promoters with reduced regulation are constitutive promoters such as, for example, the yeast TEF1 promoter, the yeast GPD promoter or the yeast PGK promoter (Mumberg D, Muller R, Funk M. (1995) Yeast vectors for the controlled expression of heterologous proteins in different genetic backgrounds. Gene. 1995 Apr. 14; 156(1):119-22; Chen C Y, Oppermann H, Hitzeman R A. (1984) Homologous versus heterologous gene expression in the yeast, Saccharomyces cerevisiae. Nucleic Acids Res. December 11; 12(23):8951-70).

The expression cassette may also contain inducible promoters, in articular a chemically inducible promoter which can be used to control expression of the nucleic acids encoding a Δ8-Δ7-isomerase, Δ5-desaturase, Δ24-reductase, HMG-CoA-reductase, lanosterol-C14-demethylase, squalene epoxidase, squalene synthetase or sterol acyltransferase in the organism at a particular time.

Promoters of this kind, such as, for example, the yeast CupI promoter (Etcheverry T. (1990) Induced expression using yeast copper metallothionein promoter. Methods Enzymol. 1990; 185:319-29.), the yeast Gall-10 promoter (Ronicke V, Graulich W, Mumberg D, Muller R, Funk M. (1997) Use of conditional promoters for expression of heterologous proteins in Saccharomyces cerevisiae, Methods Enzymol. 283:313-22) or the yeast Pho5 promoter (Bajwa W, Rudolph H, Hinnen A. (1987) PHO5 upstream sequences confer phosphate control on the constitutive PHO3 gene. Yeast. 1987 March; 3(1):33-42), may be used, for example.

A suitable terminator of the expression cassette is in principle any terminator which is able to control the expression of foreign genes in organisms, in particular in yeasts.

Preference is given to the tryptophan terminator of yeasts (TRP1 terminator).

An expression cassette is preferably prepared by fusing a suitable promoter with the above-described nucleic acids encoding a Δ8-Δ7-isomerase, Δ5-desaturase, Δ24-reductase, HMG-CoA-reductase, lanosterol-C14-demethylase, squalene epoxidase, squalene synthetase or sterol acyltransferase and, where appropriate, a terminator according to common recombination and cloning techniques as described, for example, in T. Maniatis, E. F. Fritsch and J. Sambrook, Molecular Cloning: A Laboratory Manual, Cold Spring Harbor Laboratory, Cold Spring Harbor, N.Y. (1989) and in T. J. Silhavy, M. L. Berman and L. W. Enquist, Experiments with Gene Fusions, Cold Spring Harbor Laboratory, Cold Spring Harbor, N.Y. (1984) and in Ausubel, F. M. et al., Current Protocols in Molecular Biology, Greene Publishing Assoc. and Wiley-Interscience (1987).

The nucleic acids of the invention may be prepared synthetically or obtained naturally or may contain a mixture of synthetic and natural nucleic acid components and may also comprise various heterologous gene sections of various organisms.

As described above, preference is given to synthetic nucleotide sequences with codons which are preferred by yeasts. These codons which are preferred by yeasts may be determined from codons which have the highest frequency in proteins and which are expressed in most of the interesting yeast species.

When preparing an expression cassette, it is possible to manipulate various DNA fragments in order to obtain a nucleotide sequence which expediently can be read in the correct direction and is provided with a correct reading frame. The DNA fragments may be linked to one another by attaching adaptors or linkers to said fragments.

Expediently, the promoter and terminator regions may be provided in the direction of transcription with a linker or polylinker which contains one or more restriction sites for inserting this sequence. Normally, the linker has from 1 to 10, mostly from 1 to 8, preferably from 2 to 6, restriction sites. Generally, the linker is, within the regulatory regions, less than 100 bp, frequently less than 60 bp, but at least 5 bp, in length. The promoter may be both native or homologous and non-native or heterologous to the host organism. The expression cassette preferably includes in the 5′-3′ direction of transcription the promoter, a coding nucleic acid sequence or a nucleic acid construct and a region for transcriptional termination. Various termination regions can be exchanged with one another randomly.

It is furthermore possible to use manipulations which provide appropriate restriction cleavage sites or which remove excess DNA or restriction cleavage sites. In those cases for which insertions, deletions or substitutions such as, for example, transitions and transversions are suitable, in vitro mutagenesis, primer repair, restriction or ligation can be used.

In suitable manipulations such as, for example, restriction, “chewing-back” or filling-in of protruding ends to form “blunt ends”, complementary fragment ends may be provided for ligation.

The invention further relates to the use of the above-described nucleic acids, the above-described nucleic acid constructs or the above-described proteins for preparing transgenic organisms, in particular yeasts.

Preferably, said transgenic organisms, in particular yeasts, have an increased content of 7-dehydrocholesterol and/or of the biosynthetic intermediates and/or secondary products thereof compared to the wild type.

Therefore, the invention further relates to the use of the above-described nucleic acids or the nucleic acid constructs of the invention for increasing the content of 7-dehydrocholesterol and/or of the biosynthetic intermediates and/or secondary products thereof in organisms.

The above-described proteins and nucleic acids may be used for producing 7-dehydrocholesterol and/or the biosynthetic intermediates and/or secondary products thereof in transgenic organisms.

The transfer of foreign genes into the genome of an organism, in particular of yeast, is referred to as transformation.

For this purpose, methods known per se can be used for transformation, in particular in yeasts.

Examples of suitable methods for transforming yeasts are the LiAC method as described in Schiestl R H, Gietz R D. (1989) High efficiency transformation of intact yeast cells using single stranded nucleic acids as a carrier, Curr Genet. December; 16 (5-6):339-46, electroporation as described in Manivasakam P, Schiestl R H. (1993) High efficiency transformation of Saccharomyces cerevisiae by electroporation. Nucleic Acids Res. September 11; 21(18):4414-5, and the preparation of protoplasts, as described in Morgan A J. (1983) Yeast strain improvement by protoplast fusion and transformation, Experientia Suppl. 46:155-66

The construct to be expressed is preferably cloned into a vector, in particular into plasmids which are suitable for transforming yeasts, such as, for example, the vector systems Yep24 (Naumovski L, Friedberg E C (1982) Molecular cloning of eucaryotic genes required for excision repair of UV-irradiated DNA: isolation and partial characterization of the RAD3 gene of Saccharomyces cerevisiae. J Bacteriol October; 152(1):323-31), Yep13 (Broach J R, Strathern J N, Hicks J B. (1979) Transformation in yeast: development of a hybrid cloning vector and isolation of the CAN1 gene. Gene. 1979 December; 8(1):121-33), the pRS series of vectors (Centromer and Episomal) (Sikorski R S, Hieter P. (1989) A system of shuttle vectors and yeast host strains designed for efficient manipulation of DNA in Saccharomyces cerevisiae. Genetics. May; 122(1):19-27) and the vector systems YCp19 or pYEXBX.

Accordingly, the invention furthermore relates to vectors, in particular plasmids, which comprise the above-described nucleic acids, nucleic acid constructs or expression cassettes.

The invention further relates to a method for preparing genetically modified organisms by functionally introducing an above-described nucleic acid or an above-described nucleic acid construct into the starting organism.

The invention further relates to said genetically modified organisms, the genetic modification increasing at least one of the activities selected from the group consisting of Δ8-Δ7-isomerase activity, Δ5-desaturase activity and Δ24-reductase activity, compared to a wild type.

Preferably, at least one of the activities is increased by increasing the gene expression of at least one nucleic acid selected from the group consisting of nucleic acids encoding a Δ8-Δ7-isomerase, nucleic acids encoding a Δ5-desaturase and nucleic acids encoding a Δ24-reductase.

Preferably, gene expression of the above-described nucleic acids is increased by increasing in the organism the copy number of the nucleic acids encoding a Δ8-Δ7-isomerase, encoding a Δ5-desaturase and/or encoding a Δ24-reductase.

Accordingly, the invention preferably relates to an above-described genetically modified organism which contains two or more nucleic acids encoding a Δ8-Δ7-isomerase and/or two or more nucleic acids encoding a Δ5-desaturase and/or two or more nucleic acids encoding a Δ24-reductase.

In a preferred embodiment, the genetically modified organism has, compared to the wild type, in addition to the above-described genetic modifications a reduced activity of at least one of the activities selected from the group consisting of C24-methyltransferase activity and Δ22-desaturase activity.

The reduction of at least one of the activities is preferably caused by reducing, compared to the wild type, gene expression of at least one nucleic acid selected from the group consisting of nucleic acids encoding a C24-methyltransferase and nucleic acids encoding a Δ22-desaturase.

A particularly preferred genetically modified organism has, apart from the above-described genetic modifications, no functional C24-methyltransferase gene and/or Δ22-desaturase gene.

Particular preference is given to above-mentioned genetically modified organisms in which the genetic modification additionally increases at least one of the activities selected from the group consisting of HMG-CoA-reductase activity, lanosterol-C14-demethylase activity, squalene-epoxidase activity, squalene-synthetase activity and sterol-acyltransferase activity compared to a wild type.

Preferably, at least one of these activities is increased, as mentioned above, by increasing, compared to the wild type, gene expression of at least one nucleic acid selected from the group consisting of nucleic acids encoding an HMG-CoA-reductase activity, nucleic acids encoding a lanosterol-C14-demethylase, nucleic acids encoding a squalene epoxidase, nucleic acids encoding a squalene synthetase and nucleic acids encoding a sterol acyltransferase.

Preferably, gene expression of at least one nucleic acid selected from the group consisting of nucleic acids encoding an HMG-CoA-reductase activity, nucleic acids encoding a lanosterol-C14-demethylase, nucleic acids encoding a squalene epoxidase, nucleic acids encoding a squalene synthetase and nucleic acids encoding a sterol acyltransferase is increased compared to the wild type by increasing in the organism the copy number of at least one nucleic acid selected from the group consisting of nucleic acids encoding an HMG-CoA-reductase activity, nucleic acids encoding a lanosterol-C14-demethylase, nucleic acids encoding a squalene epoxidase, nucleic acids encoding a squalene synthetase and nucleic acids encoding a sterol acyltransferase.

Accordingly, the invention preferably relates to an above-described genetically modified organism which contains two or more of at least one nucleic acid selected from the group consisting of nucleic acids encoding an HMG-CoA-reductase activity, nucleic acids encoding a lanosterol-C14-demethylase, nucleic acids encoding a squalene epoxidase, nucleic acids encoding a squalene synthetase and nucleic acids encoding a sterol acyltransferase.

In particular, the invention preferably relates to a genetically modified organism which contains, in addition to the above-described genetic modifications, two or more nucleic acids encoding an HMG-CoA-reductase and/or two or more nucleic acids encoding a lanosterol-C14-demethylase and/or two or more nucleic acids encoding a squalene epoxidase and/or two or more nucleic acids encoding a squalene synthetase and/or two or more nucleic acids encoding a sterol acyltransferase.

The above-described genetically modified organisms have, compared to the wild type, an increased content of 7-dehydrocholesterol and/or of the biosynthetic intermediates and/or secondary products thereof.

Accordingly, the invention relates to an above-described genetically modified organism which, compared to the wild type, has an increased content of 7-dehydrocholesterol and/or of the biosynthetic intermediates and/or secondary products thereof.

Preferred genetically modified organisms are yeasts or fungi which have been genetically modified according to the invention, in particular yeasts which have been genetically modified according to the invention, in particular the yeast species Saccharomyces cerevisiae which has been genetically modified according to the invention, in particular the genetically modified yeast strains Saccharomyces cerevisiae AH22, Saccharomyces cerevisiae GRF, Saccharomyces cerevisiae DBY747 and Saccharomyces cerevisiae BY4741.

In the scope of the present invention, increasing the content of 7-dehydrocholesterol and/or of the biosynthetic intermediates and/or secondary products thereof preferably means the artificially acquired ability to produce biosynthetically an increased amount of at least one of these compounds mentioned above in the genetically modified organism compared to the genetically unmodified organism.

Accordingly, as mentioned at the beginning, wild type preferably means the genetically unmodified organism, but in particular the reference organism mentioned above.

An increased content of 7-dehydrocholesterol and/or of the biosynthetic intermediates and/or secondary products thereof in comparison with the wild type means in particular the increase in the content of at least one of the abovementioned compounds in the organism by at least 50%, preferably 100%, more preferably 200%, particularly preferably 400%, in comparison with the wild type.

The content of at least one of the mentioned compounds is preferably determined according to analytical methods known per se and preferably refers to those compartments of the organism, in which sterols are produced.

The invention is illustrated by the following examples but is not limited to them:

I. General Experimental Conditions 1. Restriction

Restriction of the plasmids (1 to 10 μg) was carried out in 30 μl reaction mixtures. For this purpose, the DNA was taken up in 24 μl of H₂O and admixed with 3 μl of the appropriate buffer, 1 ml of BSA (bovine serum albumin) and 2 μl of enzyme. The enzyme concentration was 1 unit/μl or 5 units/μl, depending on the amount of DNA. In some cases, 1 μl of RNase was added to the reaction mixture in order to degrade the tRNA. The restriction mixture was incubated at 37.degree. C. for 2 hours. The restriction was monitored using a minigel.

2. Gel Electrophoreses

The gel electrophoreses were carried out in minigel or wide minigel apparatuses. The minigels (approx. 20 ml, 8 pockets) and the wide minigels (50 ml, 15 or 30 pockets) consisted of 1% strength agarose in TAE. The running buffer used was 1.times.TAE.

After adding 3 μl of stop solution, the samples (10 μl) were applied. A-DNA cut with HindIII (bands at: 23.1 kb; 9.4 kb; 6.6 kb; 4.4 kb; 2.3 kb; 2.0 kb; 0.6 kb) served as standard. For fractionation, a voltage of 80 V was applied for 45 to 60 min. Thereafter, the gel was stained in ethidium bromide solution and documented under UV light using the INTAS video documentation system or photographed using an orange filter.

3. Gel Elution

The desired fragments were isolated by means of gel elution. The restriction mixture was applied to several pockets of a minigel and fractionated. Only λ-HindIII and a “sacrifice lane” were stained in ethidium bromide solution, examined under UV light, and the desired fragment was marked. This prevented the DNA of the remaining pockets from being damaged by ethidium bromide and UV light. Putting the stained and unstained gel slices side by side made it possible to excise the desired fragment from the unstained gel slice on the basis of the marking. The agarose slice with the fragment to be isolated was introduced into a dialysis tube, sealed in air-bubble-free together with a small amount of TAE buffer and introduced into the BioRad minigel apparatus. The running buffer was 1.times.TAE and the voltage was 100 V for 40 min. Afterward, the polarity was switched for 2 min in order to redissolve DNA sticking to the dialysis tube. The buffer in the dialysis tube, which contained the DNA fragments, was transferred to reaction vessels and subjected to ethanol precipitation. For this purpose, 1/10 volume of 3M sodium acetate, tRNA (1 μl per 50 μl of solution) and 2.5 volumes of ice-cold 96% strength ethanol were added to the DNA solution. The mixture was incubated at −20.degree. C. for 30 min and then removed by centrifugation at 12 000 rpm, 4.degree. C., 30 min. The DNA pellet was dried and taken up in 10 to 50 μl of H₂O (depending on the amount of DNA).

4. Klenow Treatment

The Klenow treatment fills in protruding ends of DNA fragments, resulting in blunt ends. Per 1 μg of DNA, the following reaction mixture was pipetted: DNA .times..times. pellet+.times. 11 .times. μ .times..times. 1 .times..times. H 2 .times. 0+.times. 1.5 .times..times. 10 .times. Klenow .times..times. buffer+.times. 1 .times. μ .times..times. I .times..times. 0.1 .times..times. M .times. .times. DTT+.times. 1 .times. μ .times..times. I .times..times. nucleotide .times..times. (dNTP .times..times. 2 .times..times. mM)+.times. 1.times. μ .times..times. I .times..times. Klenow .times..times. polymerase .times..times. (1 .times..times. unit/μ .times..times. I) 25

The DNA should be from an ethanol precipitation, in order to prevent contaminations from inhibiting the Klenow polymerase. The reaction mixture was incubated at 37.degree. C. for 30 min, and the reaction was stopped by incubating for another 5 min at 70.degree. C. The DNA was recovered from the reaction mixture by ethanol precipitation and taken up in 10 μl of H₂O.

5. Ligation

The DNA fragments to be ligated were combined. The final volume of 13.1 μl contained approx. 0.5 μl of DNA with a vector/insert ratio of 1:5. The sample was incubated at 70.degree. C. for 45 seconds, cooled to room temperature (approx. 3 min) and then incubated on ice for 10 min. The ligation buffers were then added: 2.6 μl of 500 mM Tris-HCl pH 7.5 and 1.3 μl of 100 mM MgCl₂, followed by incubation on ice for a further 10 min. After adding 1 μl of 500 mM DTT and 1 μl of 10 mM ATP and another 10 min on ice, 1 μl of ligase (1 unit/pi) was added. The whole treatment should be carried out as free from vibrations as possible so that adjoining DNA ends are not separated again. The ligation was carried out at 14.degree. C. over night.

6. Transformation of E. coli

Competent Escherichia coli (E. coli) NM522 cells were transformed with the DNA of the ligation mixture. A reaction mixture containing 50 μg of the pScL3 plasmids and a reaction mixture without DNA were run as positive control and zero control, respectively. For each transformation mixture, 100 μl of 8% PEG solution, 10 μl of DNA and 200 μl of competent cells (E. coli NM522) were pipetted into a benchtop-centrifuge tube. The reaction mixtures were put on ice for 30 min and agitated occasionally.

Then the heat shock was carried out: 1 min at 42.degree. C. For regeneration, 1 ml of LB medium was added to the cells and the suspension was incubated on a shaker at 37.degree. C. for 90 min. In each case, 100 μl of the undiluted reaction mixtures, a 1:10 dilution and a 1:100 dilution were plated on LB+ampicillin plates and incubated at 37.degree. C. over night.

7. Plasmid Isolation from E. coli (Miniprep)

E. coli colonies were grown in 1.5 ml of LB+ampicillin medium in benchtop-centrifuge tubes at 37.degree. C. and 120 rpm over night. On the next day, the cells were removed by centrifugation at 5000 rpm and 4.degree. C. for 5 min and the pellet was taken up in 50 μl of TE buffer. 100 μl of 0.2 N NaOH, 1% SDS solution were added to and mixed with each reaction mixture, and the mixture was put on ice for 5 min (lysis of the cells). Then, 400 μl of Na acetate/NaCl solution (230 μl of H₂O, 130 μl of 3 M sodium acetate, 40 μl of 5M NaCl) were added, the reaction mixture was mixed and put on ice for a further 15 min (protein precipitation). After centrifugation at 11 000 rpm for 15 minutes, the supernatant containing the plasmid DNA was transferred to an Eppendorf vessel. If the supernatant was not completely clear, centrifugation was repeated. 360 μl of ice-cold isopropanol were added to the supernatant and the reaction mixture was incubated at −20.degree. C. for 30 min (DNA precipitation). The DNA was removed by centrifugation (15 min, 12 000 rpm, 4.degree. C.), the supernatant was discarded, the pellet was washed in 100 μl of ice-cold 96% strength ethanol, incubated at −20.degree. C. for 15 min and again removed by centrifugation (15 min, 12 000 rpm, 4.degree. C.). The pellet was dried in a Speed Vac and then taken up in 100 μl of H₂O. The plasmid DNA was characterized by restriction analysis. For this purpose, 10 μl of each reaction mixture were restriction-digested and fractionated gel-electrophoretically in a wide minigel (see above).

8. Plasmid Preparation from E. coli (Maxiprep)

In order to isolate larger amounts of plasmid DNA, the maxiprep method was carried out. Two flasks with 100 ml of LB+ampicillin medium were inoculated with a colony or with 100 μl of a frozen culture which carries the plasmid to be isolated and incubated at 37.degree. C. and 120 rpm over night. On the next day, the culture (200 ml) was transferred to a GSA beaker and centrifuged at 4000 rpm (2600.times.g) for 10 min. The cell pellet was taken up in 6 ml of TE buffer. The cell wall was digested by adding 1.2 ml of lysozyme solution (20 mg/ml of TE buffer) and incubated at room temperature for 10 min. Subsequently, the cells were lysed with 12 ml of a 0.2 N NaOH, 1% SDS solution, followed by incubation at room temperature for another 5 min. The proteins were precipitated by adding 9 ml of a cooled 3 M sodium acetate solution (pH 4.8) and incubation on ice for 15 minutes. After centrifugation (GSA: 13 000 rpm (27 500.times.g), 20 min, 4.degree. C.), the supernatant containing the DNA was transferred to a new GSA beaker and the DNA was precipitated with 15 ml of ice-cold isopropanol and incubation at −20.degree. C. for 30 min. The DNA pellet was washed in 5 ml of ice-cold ethanol and dried in air (approx. 30-60 min). Thereafter, it was taken up in 1 ml of H₂O. The plasmid was checked by restriction analysis. The concentration was determined by applying dilutions to a minigel. The salt content was reduced by microdialysis (pore size 0.025 μm) for 30-60 minutes.

9. Transformation of Yeast

For the transformation of yeast, a preculture of the strain Saccharomyces cerevisiae AH22 was prepared. A flask containing 20 ml of YE medium was inoculated with 100 μl of the frozen culture and incubated at 28.degree. C. and 120 rpm over night. The main culture was carried out under the same conditions in flasks containing 100 ml of YE medium which was inoculated with 10 μl, 20 μl or 50 μl of the preculture.

9.1 Preparation of Competent Cells

On the next day, the cells in the flasks were counted by means of a Thoma chamber and the flask containing from 3-5.times.10⁷ cells/ml was chosen for the subsequent procedure. The cells were harvested by centrifugation (GSA: 5000 rpm (4000.times.g) 10 min). The cell pellet was taken up in 10 ml of TE buffer and distributed into two benchtop-centrifuged tubes (5 ml each). The cells were removed by centrifugation at 6000 rpm for 3 min and then washed twice with in each case 5 ml of TE buffer. The cell pellet was then taken up in 330 μl of lithium acetate buffer per 10⁹ cells, transferred to a sterile 50 ml Erlenmeyer flask and agitated at 28.degree. C. for one hour. As a result, the cells were competent for transformation.

9.2 Transformation

For each transformation mixture, 15 μl of herring sperm DNA (10 mg/ml), 10 μl of the DNA to be transformed (approx. 0.5 μg) and 330 μl of competent cells were pipetted into a benchtop-centrifuged tube and incubated at 28.degree. C. for 30 min (without agitation). Then, 700 μl of 50% PEG 6000 were added and the suspension was incubated at 28.degree. C. for another hour, without agitation. This was followed by a heat shock at 42.degree. C. for 5 min. 100 μl of the suspension were plated on selection medium (YNB, Difco) in order to select for leucine prototrophy. In the case of selection for G418 resistance, the cells are regenerated after the heat shock (see under 9.3 Regeneration phase).

9.3 Regeneration Phase

Since the selection marker is the resistance to G418, the cells needed time to express the resistance gene. 4 ml of YE medium were added to the transformation mixtures which were then incubated on the shaker (120 rpm) at 28.degree. C. over night. On the next day, the cells were removed by centrifugation (6000 rpm, 3 min), taken up in 1 ml YE medium, and 100 μl or 200 μl thereof were plated on YE+G418 plates. The plates were incubated at 28.degree. C. for several days.

10. PCR Reaction Conditions

The reaction conditions for the polymerase chain reaction must be optimized in each individual case and do not apply absolutely to each reaction mixture. Thus it is possible, inter alia, to vary the amount of DNA used, the salt concentrations and the melting temperature. For our task, it proved advantageous to combine in an Eppendorf vessel which was suitable for use in a thermocycler the following substances: 5 μl of Super buffer, 811 of dNTPs (0.625 μM each), 5′ primer, 3′ primer and 0.2 μg of template DNA, dissolved in enough water so as to result in a total volume of 50 μl for the PCR reaction mixture, were added to 2 μl of (=0.1 U) Super Taq polymerase. The reaction mixture was briefly centrifuged and overlaid with a drop of oil. Between 37 and 40 cycles were chosen for amplification.

II. EXAMPLES Example 1

Expression and overexpression of a truncated HMG-CoA reductase, a squalene epoxidase (ERG1) and/or a lanosterol-C14-demethylase (ERG11), partially with deletion of ERG5 and ERG6 in S. cerevisiae GRF18 and GRFura3, respectively.

1.1 Preparation of the Plasmids pFlat1 and pFlat3 and pFlat4

The expression vector pFlat3 was prepared by linearizing the plasmid YEp24 (Naumovski L, Friedberg E C (1982) Molecular cloning of eucaryotic genes required for excision repair of UV-irradiated DNA: isolation and partial characterization of the RAD3 gene of Saccharomyces cerevisiae. J Bacteriol October; 152(1):323-31) via restriction with SphI and a 900 bp SphI fragment of the vector pPT2B (Lang C, Looman A C. (1995) Efficient expression and secretion of Aspergillus niger RH5344 polygalacturonase in Saccharomyces cerevisiae. Appl Microbiol Biotechnol. December; 44(1-2): 147-56) which contains the ADH1 promoter and the TRP1 terminator of the yeast Saccharomyces cerevisiae and a multiple-cloning site of the vector pUC19 (Yanisch-Perron C, Vieira J, Messing J. (1985) Improved M13 phage cloning vectors and host strains: nucleotide sequences of the M13 mp18 and pUC19 vectors. Gene. 1985; 33(1): 103-19.) was integrated.

The multiple-cloning site was extended by a polylinker containing the restriction sites NotI and XhoI. The polylinker was integrated via the SalI cleavage site of the vector. The resulting plasmid is denoted pFlat1.

The vector pFlat3 was prepared by linearizing the vector pFlat1 by the enzyme NcoI and blunt-ending it by means of Klenow treatment. This was followed by integrating a BamHI fragment which had been blunt-ended by means of Klenow-polymerase treatment and which contains the yeast LEU2 gene and originates from the plasmid YDpL (Berben, G., Dumont, J., Gilliquet, V., Bolle, P. A. and Hilger F. (1991) The YDp Plasmids: a Uniform Set of Vectors Bearing Versatile Disruption Cassettes for Saccharomyces cerevisiae. Yeast 7: 475-477.).

The vector pFlat4 was prepared by linearizing the vector pFlat1 by the enzyme NcoI and blunt-ending it by means of Klenow treatment. This was followed by integrating a BamHI fragment which had been blunt-ended by means of Klenow-polymerase treatment and which contains the yeast HIS3 gene and originates from plasmid YDpH (Berben et al., 1991).

1.2 Integration of ERG1, ERG11, ERG4, ERG2 or ERG3 or of the Δ24-Reductase Gene into the Vectors pFLat1, pFlat3 and pFlat4

First, a NotI restriction cleavage site was inserted at the 5′-coding side of the genes ERG1, ERG11, ERG4, Δ24-reductase, ERG2 or ERG3 and an XhoI restriction cleavage site was inserted at the 3′-coding side of said genes by means of PCR and the corresponding coding regions were amplified. Subsequently, the amplicons were treated with the restriction enzymes NotI and XhoI. The plasmids pFlat1, pFlat3 and pFlat4 were treated in parallel with enzymes NotI and XhoI. The cleaved amplicons were then integrated into the cleaved plasmids via ligation using T4 ligase. FIG. 7 depicts as an example the plasmid pFLAT-3-ERG4.

Primer sequences for cloning ERG1, ERG11, ERG2, ERG3, ERG4, Δ24- reductase: TABLE-US-00002 Primer ERG1-5′ (SEQ. ID. No. 51): CTGCGGCCGC ATCATGTCTG CTGTTAACGT TGC Primer ERG1-3′ (SEQ. ID. No. 52): TTCTCGAGTT AACCAATCAA CTCACCAAAC Primer ERG11-5′ (SEQ. ID. No. 53): CTGCGGCCGCAGGATGTCTGCTACCAAGTCAATCG Primer ERG11-3′ (SEQ. ID. No. 54): ATCTCGAGCTTAGATCTTTTGTTCTGGATTTCTC Primer ERG2-5′ (SEQ. ID. No. 55): CTGCGGCCGCACCATGAAGTTTTTCCCACT CC Primer ERG2-3′ (SEQ. ID. No. 56): TTCTCGAGTTAGAACTTTTTGTTTTGCAACAAG Primer ERG3-5′ (SEQ. ID. No. 57): CTGCGGCCGCAATATGGATTTGGTCTTAGAAGTCG Primer ERG3-3′ (SEQ. ID. No. 58): AACTCGAGTCAGTTGTTCTTCTTGGTATTTG Primer ERG4-5′ (SEQ. ID. No. 59): CTGCGGCCGCACTATGGCAAAGGATAATAGTGAG Primer ERG4-3′ (SEQ. ID. No. 60): TTCTCGAGCTAGAAAACATAAGGAATAAAGAC Primer Δ24R-5′ (SEQ. ID. No. 47): CTGCGGCCGCAAGATGGAGCCCGCCGTGTCGC Primer Δ24R-3′ (SEQ. ID. No. 48) AACTCGAGTCAGTGCCTTGCCGCCTTGC 1.3 Preparation of the Integration Vectors pUG6-tHMG, pUG6-ERG1, pUG6-ERG11 1.3.1 pUG6-tHMG

The DNA sequence for the expression cassette composed of ADH1-promoter-tHMG-tryptophan-terminator was isolated from the vector YepH2 (Polakowski, T., Stahl, U., Lang, C. (1998): Overexpression of a cytosolic HMG-CoA reductase in yeast leads to squalene accumulation. Appl. Microbiol. Biotechnol. 49: 66-71) by restriction with the enzymes EcoRV and Bsp68I (NruI) by using standard methods. The DNA fragment obtained was cloned with blunt ends into the EcoRV cleavage site of the vector pUG6 (Guldener, U et al. (1996): A new efficient gene disruption cassette for repeated use in budding yeast, Nucleic Acids Res. July 1; 24(13):2519-24), resulting in the vector denoted pUG6-tHMG (FIG. 1).

1.3.2 pUG6-ERG1

The DNA sequence for the expression cassette composed of ADH1-promoter-ERG1-tryptophan-terminator was isolated from the vector pFlat3-ERG1 by restriction with the enzymes NheI and Bsp68I (NruI), using standard methods. After Klenow treatment, the DNA fragment obtained was cloned with blunt ends into the EcoRV cleavage site of the vector pUG6 (Guldener, U et al. (1996): A new efficient gene disruption cassette for repeated use in budding yeast, Nucleic Acids Res. July 1; 24(13):2519-24), resulting in the vector denoted pUG6-ERG1 (FIG. 2).

1.3.3 pUG6-ERG11

The DNA sequence for the expression cassette composed of ADH1-promotor-ERG11-tryptophan-terminator was isolated from the vector pFlat3-ERG11 by restriction with the enzymes EcoRV and Bsp68I (NruI) using standard methods. The DNA fragment obtained was cloned with blunt ends into the EcoRV cleavage site of the vector pUG6 (Guldener, U et al. (1996): A new efficient gene disruption cassette for repeated use in budding yeast, Nucleic Acids Res. July 1; 24(13):2519-24), resulting in the vector denoted pUG6-ERG11 (FIG. 3).

1.4. Integrative Transformation of the Expression Cassettes into the Yeast Strains GRF or GRFura3

After plasmid isolation, fragments of the vectors pUG6-tHMG, pUG6-ERG1 and pUG6-ERG11 were amplified by means of PCR in such a way that the resulting fragments consist of the following components: loxP-kanMX-loxP-ADH1 promoter-target gene-tryptophan terminator, with target gene meaning tHMG, ERG1 and, ERG11 and kanMX respectively, meaning a kanamycin-resistance gene.

The selected primers were oligonucleotide sequences which contain in the annealing region the sequences beyond the cassettes to be amplified of the vector pUG6-target gene and which contain at the 5′ and 3′ protruding ends in each case 40 base pairs of the 5′ or 3′ sequence of the integration locus. This ensures that on the one hand the entire fragment, including KanMX and target gene, is amplified and, on the other hand, this fragment can then be transformed into yeast and be integrated by homologous recombination into the target gene locus of the yeast. Depending on the target gene locus in the yeast, the following oligonucleotide sequences were used as primers:

For integration at the URA3 gene locus: TABLE-US-00003 For integration at the URA3 gene locus: URA3-Crelox-5′ (SEQ. ID. No. 33): 5′-ATGTCGAAAG CTACATATAA GGAACGTGCT GCATCTCATC CCAGCTGAAG CTTCGTACGC-3′ URA3-Crelox-3′ (SEQ. ID. No. 34): 5′-TTAGTTTTGC TGGCCGCATC TTCTCAAATA TGCTTCCCAG GCATAGGCCA CTAGTGGATC TG-3′ For integration at the LEU2 gene locus: LEU2-Crelox-5′ (SEQ. ID. No. 35): 5′-GAATACTCAG GTATCGTAAG ATGCAAGAGT TCGAATCTCT CCAGCTGAAG CTTCGTACGC-3′ LEU2-Crelox-3′ (SEQ. ID. No. 36): 5′-TCTACCCTAT GAACATATTC CATTTTGTAA TTTCGTGTCG GCATAGGCCA CTAGTGGATC TG-3′ For integration at the HIS3 gene locus: TABLE-US-00004 HIS3-Crelox-5′ (SEQ. ID. No. 37): 5′-ATGACAGAGC AGAAACCCCT AGTAAAGCGT ATTACAAATG CCAGCTGAAG CTTCGTACGC-3′ HIS3-Crelox-3′ (SEQ. ID. No. 38): 5′-CTACATAAGA ACACCTTTGG TGGAGGGAAC ATCGTTGGTA GCATAGGCCA CTAGTGGATC TG-3′ For integration at the ERG6 gene locus: TABLE-US-00005 ERG6-Crelox-5′ (SEQ. ID. No. 39): 5′-ATGAGTGAAA CAGAATTGAG AAAAAGACAG GCCCAATTCA CCAGCTGAAG CTTCGTACGC-3′ ERG6-Crelox-3′ (SEQ. ID. No. 40): 5′-TTATTGAGTT GCTTCTTGGG AAGTTTGGGA GGGGGTTTCG GCATAGGCCA CTAGTGGATC TG-3′ For integration at the ERG5 gene locus: TABLE-US-00006 ERG5-Crelox-5′ (SEQ. ID. No. 41): 5′-ATGAGTTCTG TCGCAGAAAA TATAATACAA CATGCCACTC CCAGCTGAAG CTTCGTACGC-3′ ERG5-Crelox-3′ (SEQ. ID. No. 42): 5′-TTATTCGAAG ACTTCTCCAG TAATTGGGTC TCTCTTTTTG GCATAGGCCA CTAGTGGATC TG-3′

The resistance to Geneticin (G418) served as selection marker. The resulting strains contained a copy of the particular target gene (tHMG, ERG1 or ERG11) under the control of the ADH promoter and the tryptophan terminator. At the same time, it was possible to delete the particular gene of the target locus by integrating the expression cassette. In order to subsequently remove again the gene for G418 resistance, the resultant yeast strain was transformed with the cre recombinase-containing vector pSH47 (Guldener U, Heck S, Fielder T, Beinhauer J, Hegemann J H. (1996) A new efficient gene disruption cassette for repeated use in budding yeast. Nucleic Acids Res. July 1; 24(13):2519-24). This vector caused the expression of cre recombinase in the yeast, and, as a consequence, the sequence region within the two loxP sequences was removed by recombination, and this in turn resulted in only one of the two loxP sequences and the ADH1 promoter-target gene-tryptophan terminator expression cassette remaining in the target gene locus.

As a consequence, the yeast strain loses its G418 resistance again and is therefore suitable for integrating or removing further genes by means of this “cre-lox” system into or from said yeast strain. The vector pSH47 can then be removed selectively by cultivation on FOA medium.

Thus it is possible to integrate a plurality of target genes successively into the yeast strain under the control of the ADH1 promoter and tryptophan terminator at various target loci.

First, a target gene is integrated at the URA3 locus or a ura3 strain is used in order to render the yeast strain uracil-auxotrophic, since the vector pSH47 contains a URA3 gene for selection of uracil-prototrophic strains. FIG. 4 shows an example of the method.

This method produced the yeast integration and deletion strains listed in Table 1, with, in a manner known per se, the gene in lower-case letters representing a deletion and the gene in capital letters representing an integration.

TABLE 1 Modification No. Strain name No. Strain name compared to GRF yeast strain I GRFtH1 ura3, tHMG: leu2 II GRFth1e1 ERG1: ura3, tHMG: leu2 III GRFtH1E11 ura3, tHMG: leu2, ERG11: his3 IV GRFtH1E1E11 ERG1: ura3, tHMG: leu2, ERG11: his3 V GRFtH1E1E11erg5erg6 ura3, tHMG: leu2, ERG1: erg6, ERG11: erg5 VI GRFtH1erg5erg6 ura3, tHMG: leu2, erg5, ergG

The yeast strains were cultured in a culture volume of 20 ml in WMVIII medium at 28.degree. C. and 160 rpm for 48 hours. Subsequently, 500 μl of this preculture were transferred to a 50 ml main culture of the same medium and cultured in a baffled flask at 28.degree. C. and 160 rpm for 3 days.

After 3 days, the sterols and squalene were extracted (Parks L W, Bottema C D, Rodriguez R J, Lewis T A. (1985) Yeast sterols: yeast mutants as tools for the study of sterol metabolism. Methods Enzymol. 1985; 111:333-46.) and analyzed by means of gas chromatography. The following values were obtained (see Table 2).

Content of sterols 1 to 11 in [peak area/gTS] No. Strain name 1 2 3 4 5 6 7 8 9 10 11 I GRFtH1 9.9 0.8 0.3 1.2 1.1 1.0 0.0 0.0 0.0 0.0 4.7 II GRFtH1E1 6.8 1.9 0.4 1.5 2.2 2.1 0.0 0.0 0.0 0.0 6.9 III GRFtH1E11 9.9 0.4 0.7 2.3 1.9 1.9 0.0 0.0 0.0 0.0 5.0 IV GRFtH1E1E11 6.0 1.2 0.9 3.0 2.3 2.2 0.0 0.0 0.0 0.0 7.2 V GRFtH1E1E11 5.8 0.8 0.4 23.1 0.0 0.0 0.0 0.0 11.8 0.0 0.0 erg5erg6 VI GRFtH1erg5erg6 9.9 0.8 0.3 12.6 0.0 0.0 0.0 0.0 7.1 0.0 0.0 1 = Squalene 2 = Lanosterol 3 = Dimethylzymosterol 4 = Zymosterol 5 = Fecosterol 6 = Episterol 7 = Cholesta-7,24-dienol 8 = Cholesta-8-enol 9 = Cholesta-5,7,24 trienol 10 = 7-Dehydrocholesterol 11 = Ergosterol

Example 2 Expression of the Heterologous Gene Encoding a Δ8-Δ7-Isomerase (Ebp) from Mice (Mus musculus) in Yeast

The cDNA sequence of Mus musculus Δ8-Δ7-isomerase (Moebius, F. F., Soellner, K. E. M., Fiechter, B., Huck, C. W., Bonn, G., Glossmann, H. (1999): Histidine77, Glutamic Acid123, Threonine126, Asparagine194, and Tryptophan197 of Human Emopamil Protein Are Required for in Vivo Sterol Δ8-Δ7 Isomerisation. Biochem. 38, 1119-1127) was amplified by PCR from the cDNA clone IMAGp998A22757 (Host: E. coli DH10B) of the Deutsches Resourcenzentrum fur Genomforschung [German resource center for genome research] GmbH (Berlin).

The primers used here are the DNA oligomers Ebp-5′ (SEQ. ID. No. 43) and Ebp-3′ (SEQ. ID. No. 44). The DNA fragment obtained was treated with restriction enzymes NotI and XhoI and then integrated into the vectors pFlat3 and pFlat1 (FIG. 4) which likewise been treated with the enzymes NotI and XhoI beforehand by means of a ligase reaction. The resulting vectors pFlat1-EBP and pFlat3-EBP (FIG. 5 a) contain the EBP gene under the control of the ADH promoter and the tryptophan terminator.

The expression vector pFlat3-EBP was then transformed into the yeast strains I to VI of Table 1 from Example 1 and also into the GRFura3 strain. The yeast strains obtained in this way were then cultured in a culture volume of 20 ml in WMVIII medium at 28.degree. C. and 160 rpm for 48 hours. Subsequently, 500 μl of this preculture were transferred to a 50 ml main culture of the same medium and cultured in a baffled flask at 28.degree. C. and 160 rpm for 3 days.

The sterols were extracted after 3 days and analyzed by means of gas chromatography, as described in Example 1. The influence of the expression of a Mus musculus Δ8-Δ7-isomerase in combination with the expression of the transcriptionally deregulated intrinsic yeast genes tHMG and/or ERG1 and/or ERG11 and/or deletion of the intrinsic yeast genes ERG6 and ERG5 is listed in Table 3. The abbreviations have the following meanings: −=decrease; 0=no change; /=not present; +, ++, +++, ++++=concentrated to highly concentrated.

Influence of the genetic modifications on the sterol content compared to the GRF yeast strain No. Strain name 1 2 3 4 5 6 7 8 9 10 11 VII GRFtH1 0 0 0 0 0 0 / / / / 0 pFlat3-Ebp VIIII GRFtH1E1 0 0 0 − 0 0 + / / / 0 pFlat3-Ebp IX GRFtH1E11 pFlat3- 0 0 0 − 0 0 + / / / 0 Ebp X GRFtH1E1E11 pFlat3- 0 0 0 − 0 0 + / / / 0 Ebp XI GRFtH1E1E11erg5erg6 0 0 0 − / / + / ++ / / pFlat3-Ebp XII GRFtH1erg5erg6 0 0 0 − / / + / + / / pFlat3-Ebp 1 = Squalene 2 = Lanosterol 3 = Dimethylzymosterol 4 = Zymosterol 5 = Fecosterol 6 = Episterol 7 = Cholesta-7,24-dienol 8 = Cholesta-8-enol 9 = Cholesta-5,7,24 trienol 10 = 7-Dehydrocholesterol 11 = Ergosterol

Example 3 Expression of the Heterologous Gene Encoding a Δ5-Desaturase (Sc5d) from Mice (Mus musculus) in Yeast

The cDNA sequence of Mus musculus Δ5-desaturase (Nishi, S., Hideaki, N., Ishibashi, T. (2000): cDNA cloning of the mammalian sterol C5-desaturase and the expression in yeast mutant. Biochim. Biophys. A 1490, 106-108) was amplified by PCR from the cDNA clone IMAGp998K144618 (Host: E. coli DH10B) of the Deutsches Resourcenzentrum fur Genomforschung [German resource center for genome research] GmbH (Berlin). The primers used here are the DNA oligomers Sc5d-5′ (SEQ. ID. No. 45) and Sc5d-3′ (SEQ. ID. No. 46). The DNA fragment obtained was treated with restriction enzymes NotI and XhoI and then integrated into the vector pFlat3 (FIG. 4) which likewise had been treated with the enzymes NotI and XhoI beforehand, by means of a ligase reaction. The resulting vector pFlat3-SC5D (FIG. 5 b) contains the SC5D gene under the control of the ADH promoter and the tryptophan terminator.

The expression vector pFlat3-SC5D was then transformed into the yeast strains Ito VI of Table 1 from Example 1 and also into the GRFura3 strain. The yeast strains obtained in this way were then cultured in a culture volume of 20 ml in WMVIII medium at 28.degree. C. and 160 rpm for 48 hours. Subsequently, 500 μl of this preculture were transferred to a 50 ml main culture of the same medium and cultured in a baffled flask at 28.degree. C. and 160 rpm for 3 days.

The sterols were extracted after 3 days and analyzed by means of gas chromatography, as described in Example 1. The influence of the expression of a Mus musculus Δ5-desaturase in combination with the expression of the transcriptionally deregulated intrinsic yeast genes tHMG and/or ERG1 and/or ERG11 and/or deletion of the intrinsic yeast genes ERG6 and ERG5 is listed in Table 4. The abbreviations have the following meanings: −=decrease; 0=no change; /=not present; +, ++, +++, ++++=concentrated to highly concentrated.

TABLE 4 Influence of the genetic modifications on the sterol content compared to the GRF yeast strain No. Strain name 1 2 3 4 5 6 7 8 9 10 11 XIII GRFtH1 pFlat3-Sc5d 0 0 0 0 0 0 / / / / 0 XIV GRFtH1E1 pFlat3-Sc5d 0 0 0 − 0 0 / / + / 0 XV GRFtH1E11 0 0 0 − 0 0 / / + / 0 pFlat3-Sc5d XVI GRFtH1E1E11 0 0 0 − 0 0 / / + / 0 pFlat3-Sc5d XVII GRFtH1E1E11erg5erg6 0 − 0 −− / / / / +++ + / pFlat3-Sc5d XVIII GRFtH1erg5erg6 0 0 0 −− / / / / ++ / / pFlat3-Sc5d 1 = Squalene 2 = Lanosterol 3 = Dimethylzymosterol 4 = Zymosterol 5 = Fecosterol 6 = Episterol 7 = Cholesta-7,24-dienol 8 = Cholesta-8-enol 9 = Cholesta-5,7,24 trienol 10 = 7-Dehydrocholesterol 11 = Ergosterol

Example 4 Expression of the Heterologous Gene Encoding a Δ24-Reductase (D24R) from Mice (Mus musculus) in Yeast

The cDNA sequence of Mus musculus Δ24-reductase (Waterham, H. R., Koster, J., Romeijn, G. J., Hennekam, R. C., Vreken, P., Andersson, H. C., FitzPatrick, D. R., Kelley, R. I. and Wanders, R. J., Mutations in the 3β-Hydroxysterol Δ24-Reductase Gene Cause Desmosterolosis, an Autosomal Recessive Disorder of Cholesterol Biosynthesis, Am. J. Hum. Genet. 69 (4), 685-694 (2001)) was amplified by PCR from the cDNA clone IMAGp998K179532 (Host: E. coli DH10B) of the Deutsches Resourcenzentrum fur Genomforschung [German resource center for genome research] GmbH (Berlin).

The primers used here are the DNA oligomers D24R-5′ (SEQ. ID. No. 47) and D24R-3′ (SEQ. ID. No. 48). The DNA fragment obtained was treated with restriction enzymes NotI and XhoI and then integrated into the vector pFlat4 (FIG. 6) which likewise had been treated with the enzymes NotI and XhoI beforehand, by means of a ligase reaction. The resulting vector pFlat4-D24R (FIG. 5 d) contains the D24R gene under the control of the ADH1 promoter and the tryptophan terminator.

The expression vector pFlat4-D24R was then transformed into the yeast strains I to VI of Table 1 from Example 1 and also into the GRFura3 strain. The yeast strains obtained in this way were then cultured in a culture volume of 20 ml in WMVIII medium at 28.degree. C. and 160 rpm for 48 hours. Subsequently, 500 μl of this preculture were transferred to a 50 ml main culture of the same medium and cultured in a baffled flask at 28.degree. C. and 160 rpm for 3 days.

The sterols were extracted after 3 days and analyzed by means of gas chromatography, as described in Example 1. The influence of the expression of a Mus musculus Δ24-reductase in combination with the expression of the transcriptionally deregulated intrinsic yeast genes tHMG and/or ERG1 and/or ERG11 and/or deletion of the intrinsic yeast genes ERG6 and ERG5 is listed in Table 5. The abbreviations have the following meanings: −=decrease; 0=no change; /=not present; +, ++, +++, ++++=concentrated to highly concentrated.

TABLE 5 Influence of the genetic modifications on the sterol content compared to the GRF yeast strain No. Strain name 1 2 3 4 5 6 7 8 9 10 11 XIX GRFtH1 0 0 0 0 0 0 / / / / 0 pFlat4-D24R XX GRFtH1E1 0 − − − 0 0 / / / + 0 pFlat4-D24R XXI GRFtH1E11 pFlat4- 0 0 0 − 0 0 / + / + 0 D24R XXII GRFtH1E1E11 pFlat4- 0 0 0 − 0 0 / + / + 0 D24R XXIII GRFtH1E1E11erg5erg6 0 − − −− / / 0 + + +++ / pFlat4-D24R XXIV GRFtH1erg5erg6 0 − − − / / 0 + + ++ / pFlat4-D24R 1 = Squalene 2 = Lanosterol 3 = Dimethylzymosterol 4 = Zymosterol 5 = Fecosterol 6 = Episterol 7 = Cholesta-7,24-dienol 8 = Cholesta-8-enol 9 = Cholesta-5,7,24 trienol 10 = 7-Dehydrocholesterol 11 = Ergosterol

Example 5 Coexpression of the Heterologous Genes Encoding a Δ8-Δ7-Isomerase (Ebp) from Mice (Mus musculus) and a C5-Desaturase (Sc5d) from Mice (Mus musculus) in Yeast

The expression vectors pFlat1-EBP (from Example 2) and pFlat3-SC5D (from Example 3) were transformed into the yeast strains I to VI of Table 1 of Example 1 and also into the GRFura3 strain. The yeast strains obtained in this way were then cultured in a culture volume of 20 ml in WMVIII medium at 28.degree. C. and 160 rpm for 48 hours. Subsequently, 500 μl of this preculture were transferred to a 50 ml main culture of the same medium and cultured in a baffled flask at 28.degree. C. and 160 rpm for 3 days.

The sterols were extracted after 3 days and analyzed by means of gas chromatography, as described in Example 1. The influence of the expression of a Δ8-Δ7-isomerase and a Mus musculus C5-desaturase in combination with the expression of the transcriptionally deregulated intrinsic yeast genes tHMG and/or ERG1 and/or ERG11 and/or deletion of the intrinsic yeast genes ERG6 and ERG5 is listed in Table 6. The abbreviations have the following meanings: −=decrease; 0=no change; /=not present; +, ++, +++, ++++=concentrated to highly concentrated.

TABLE 6 Influence of the genetic modifications on the sterol content compared to the GRF yeast strain No. Strain name 1 2 3 4 5 6 7 8 9 10 11 VVX GRFtH1 pFlat3-Ebp/ 0 0 0 − 0 0 / / + / 0 pFlat1-Sc5d XXVI GRFtH1E1 pFlat3-Ebp/ 0 − 0 −− 0 0 / / + / 0 pFlat1-Sc5d XXVII GRFtH1E11 pFlat3- 0 0 0 −− 0 0 / / + / 0 Ebp/pFlat1-Sc5d XXVIII GRFtH1E1E11 pFlat3- 0 − − −− 0 0 / / ++ / 0 Ebp/pFlat1-Sc5d XXIX GRFtH1E1E11erg5erg6 0 − 0 −− / / / / +++ + / pFlat3-Ebp/pFlat1- Sc5d XXX GRFtH1erg5erg6 0 0 0 − / / / / ++ + / pFlat3-Ebp/pFlat1- Sc5d 1 = Squalene 2 = Lanosterol 3 = Dimethylzymosterol 4 = Zymosterol 5 = Fecosterol 6 = Episterol 7 = Cholesta-7,24-dienol 8 = Cholesta-8-enol 9 = Cholesta-5,7,24 trienol 10 = 7-Dehydrocholesterol 11 = Ergosterol

Example 6

Coexpression of the Heterologous Genes Encoding a Δ8-Δ7-Isomerase (Ebp) from Mice (Mus musculus) Encoding a C5-Desaturase (Sc5d) from Mice (Mus musculus) and a Δ24-Reductase from Mice (Mus musculus) in Yeast

The expression vectors pFlat1-EBP (from Example 2) and pFlat3-SC5D (from Example 3) and pFlat4-D24R (from Example 4) were transformed into the yeast strains Ito VI of Table 1 of Example 1 and also into the GRFura3 strain. The yeast strains obtained in this way were then cultured in a culture volume of 20 ml in WMVIII medium at 28.degree. C. and 160 rpm for 48 hours. Subsequently, 500 μl of this preculture were transferred to a 50 ml main culture of the same medium and cultured in a baffled flask at 28.degree. C. and 160 rpm for 3 days.

The sterols were extracted after 3 days and analyzed by means of gas chromatography, as described in Example 1. The influence of the expression of a Δ8-Δ7-isomerase, a Mus musculus C5-desaturase and a Mus musculus E in combination with the expression of the transcriptionally deregulated intrinsic yeast genes tHMG and/or ERG1 and/or ERG11 and/or deletion of the intrinsic yeast genes ERG6 and ERG5 is listed in Table 7. The abbreviations have the following meanings: −=decrease; 0=no change; /=not present; ++, +++, ++++=concentrated to highly concentrated.

TABLE 7 Influence of the genetic modifications on the sterol content compared to the GRF yeast strain No. Strain name 1 2 3 4 5 6 7 8 9 10 11 XXXI GRFtH1 pFlat3-Ebp/ 0 0 0 − 0 0 / / / + 0 pFlat1-Sc5d/pFlat4- D24R XXXII GRFtH1E1 pFlat3-Ebp/ 0 − 0 −− 0 0 / / / + 0 pFlat1-Sc5d/pFlat4- D24R XXXIII GRFtH1E11 pFlat3- 0 0 0 −− 0 0 / / / + 0 Ebp/pFlat1-Sc5d/ pFlat4-D24R XXXIV GRFtH1E1E11 pFlat3- 0 − − −− 0 0 / / / + 0 Ebp/pFlat1-Sc5d/ pFlat4-D24R XXXV GRFtH1E1E11erg5erg6 0 − 0 −−− / / / / + ++++ / pFlat3-Ebp/pFlat1- Sc5d/pFlat4-D24R XXXVI GRFtH1erg5erg6 0 0 0 − / / / / ++ +++ / pFlat3-Ebp/pFlat1- Sc5d/pFlat4-D24R 1 = Squalene 2 = Lanosterol 3 = Dimethyl zymosterol 4 = Zymosterol 5 = Fecosterol 6 = Episterol 7 = Cholesta-7,24-dienol 8 = Cholesta-8-enol 9 = Cholesta-5,7,24 trienol 10 = 7-Dehydrocholesterol 11 = Ergosterol 

1. A method for preparing 7-dehydrocholesterol and/or the biosynthetic intermediates and/or secondary products thereof by culturing organisms which, compared to the wild type, have an increased activity of at least one of the activities selected from the group consisting of Δ8-Δ7-isomerase activity, Δ5-desaturase activity and Δ24-reductase activity.
 2. The method of claim 1, wherein the organisms, compared to the wild type, have an increased activity of at least two of the activities selected from the group consisting of Δ8-Δ7-isomerase activity, Δ5-desaturase activity and Δ24-reductase activity.
 3. The method of claim 1, wherein the organisms, compared to the wild type, have an increased Δ8-Δ7-isomerase activity, Δ5-desaturase activity and Δ24-reductase activity.
 4. The method of claim 1, wherein the Δ8-Δ7-isomerase activity is increased by increasing, compared to the wild type, gene expression of a nucleic acid encoding a Δ8-Δ7-isomerase.
 5. The method of claim 4, wherein gene expression is increased by introducing into the organism one or more nucleic acids encoding a 48-47-isomerase.
 6. The method of claim 5, wherein nucleic acids are introduced, which encode proteins comprising the amino acid sequence SEQ. ID. NO. 2 or a sequence derived from this sequence by substitution, insertion or deletion of amino acids, which is at least 30% identical at the amino acid level with the sequence SEQ. ID. NO. 2, and having the enzyme property of a Δ8-Δ7-isomerase.
 7. The method of claim 6, which comprises introducing a nucleic acid comprising the sequence SEQ. ID. NO.
 1. 8. The method of claim 1, wherein the Δ5-desaturase activity is increased by increasing, compared to the wild type, gene expression of a nucleic acid encoding a Δ5-desaturase.
 9. The method of claim 8, wherein gene expression is increased by introducing into the organism one or more nucleic acids encoding a 45-desaturase.
 10. The method of claim 9, wherein nucleic acids are introduced, which encode proteins comprising the amino acid sequence SEQ. ID. NO. 4 or a sequence derived from this sequence by substitution, insertion or deletion of amino acids, which is at least 30% identical at the amino acid level with the sequence SEQ. ID. NO. 4, and having the enzyme property of a Δ5-desaturase.
 11. The method of claim 10, which comprises introducing a nucleic acid comprising the sequence SEQ. ID. NO.
 3. 12. The method of claim 1, wherein the Δ24-reductase activity is increased by increasing, compared to the wild type, gene expression of a nucleic acid encoding a Δ24-reductase.
 13. The method of claim 12, wherein gene expression is increased by introducing into the organism one or more nucleic acids encoding a Δ24-reductase.
 14. The method of claim 13, wherein nucleic acids are introduced, which encode proteins comprising the amino acid sequence SEQ. ID. NO. 6 or a sequence derived from this sequence by substitution, insertion or deletion of amino acids, which is at least 30% identical at the amino acid level with the sequence SEQ. ID. NO. 6, and having the enzymic property of a Δ24-reductase.
 15. The method of claim 14, which comprises introducing a nucleic acid comprising the sequence SEQ. ID. NO.
 5. 16. The method of claim 1, wherein the organisms, compared to the wild type, additionally have a reduced activity of at least one of the activities selected from the group consisting of C24-methyltransferase activity and Δ22-desaturase activity.
 17. The method of claim 16, wherein the organisms, compared to the wild type, have a reduced C24-methyltransferase activity and a reduced 422-desaturase activity.
 18. The method of claim 16, wherein the C24-methyltransferase activity is reduced by reducing, compared to the wild type, gene expression of a nucleic acid encoding a C24-methyltransferase.
 19. The method of claim 18, wherein an organism is used, which has no functional C24-methyltransferase gene.
 20. The method of claim 16, wherein the Δ22-desaturase activity is reduced by reducing, compared to the wild type, gene expression of a nucleic acid encoding a Δ22-desaturase.
 21. The method of claim 20, wherein an organism is used, which has no functional Δ22-desaturase gene.
 22. The method of claim 1, wherein the organisms additionally have, compared to the wild type, an increased activity of at least one of the activities selected from the group consisting of HMG-CoA-reductase activity, lanosterol C14-demethylase activity, squalene-epoxidase activity, squalene-synthetase activity and sterol-acyltransferase activity.
 23. The method of claim 22, wherein the organisms additionally have, compared to the wild type, an increased lanosterol C14-demethylase activity and an increased HMG-CoA-reductase activity.
 24. The method of claim 22, wherein the lanosterol C14-demethylase activity is increased by increasing, compared to the wild type, gene expression of a nucleic acid encoding a lanosterol C14-demethylase.
 25. The method of claim 24, wherein gene expression is increased by introducing into the organism one or more nucleic acids encoding a lanosterol C14-demethylase.
 26. The method of claim 25, wherein nucleic acids are introduced, which encode proteins comprising the amino acid sequence SEQ. ID. NO. 8 or a sequence derived from this sequence by substitution, insertion or deletion of amino acids, which is at least 30% identical at the amino acid level with the sequence SEQ. ID. NO. 8, and having the enzymic property of a lanosterol C14-demethylase.
 27. The method of claim 26, which comprises introducing a nucleic acid comprising the sequence SEQ. ID. NO.
 7. 28. The method of claim 22, wherein the HMG-CoA-reductase activity is increased by increasing, compared to the wild type, gene expression of a nucleic acid encoding an HMG-CoA reductase.
 29. The method of claim 28, wherein gene expression is increased by introducing into the organism a nucleic acid construct comprising a nucleic acid which encodes an HMG-CoA reductase and whose expression in said organism, in comparison with the wild type, is subject to a reduced regulation.
 30. The method of claim 29, wherein the nucleic acid construct contains a promoter which, in comparison with the wild-type promoter, is subjected to a reduced regulation in the organism.
 31. The method of claim 29, wherein the HMG-CoA reductase-encoding nucleic acid used is a nucleic acid whose expression in the organism, in comparison with the orthologous nucleic acid intrinsic to said organism, is subject to a reduced regulation.
 32. The method of claim 31, wherein the HMG-CoA reductase-encoding nucleic acid used is a nucleic acid which encodes the catalytic region of said HMG-CoA reductase.
 33. The method of claim 32, wherein nucleic acids are introduced, which encode proteins comprising the amino acid sequence SEQ. ID. NO. 10 or a sequence derived from this sequence by substitution, insertion or deletion of amino acids, which is at least 30% identical at the amino acid level with the sequence SEQ. ID. NO. 10, and having the enzyme property of a HMG-CoA reductase.
 34. The method of claim 33, which comprises introducing a nucleic acid comprising the sequence SEQ. ID. NO.
 9. 35. The method of claim 22, wherein an organism is used which, compared to the wild type, additionally has an increased squalene-epoxidase activity.
 36. The method of claim 35, wherein the squalene-epoxidase activity is increased by increasing, compared to the wild type, gene expression of a nucleic acid encoding a squalene epoxidase.
 37. The method of claim 36, wherein gene expression is increased by introducing into the organism one or more nucleic acids encoding a squalene epoxidase.
 38. The method of claim 37, wherein nucleic acids are introduced, which encode proteins comprising the amino acid sequence SEQ. ID. NO. 12 or a sequence derived from this sequence by substitution, insertion or deletion of amino acids, which is at least 30% identical at the amino acid level with the sequence SEQ. ID. NO. 12, and having the enzyme property of a squalene epoxidase.
 39. The method of claim 38, which comprises introducing a nucleic acid comprising the sequence SEQ. ID. NO.
 11. 40. The method of claim 1, wherein the organism used is yeast.
 41. The method of claim 1, which comprises harvesting the organism, after culturing, and then isolating 7-dehydrocholesterol and/or the biosynthetic intermediates and/or secondary products thereof from said organism.
 42. A nucleic acid construct, comprising at least one nucleic acid selected from the group consisting of nucleic acids encoding a Δ8-Δ7-isomerase, nucleic acids encoding a Δ5-desaturase and nucleic acids encoding a Δ24-reductase, which are functionally linked with one or more regulatory signals ensuring transcription and translation in organisms.
 43. A nucleic acid construct of claim 42, additionally comprising at least one nucleic acid selected from the group consisting of nucleic acids encoding an HMG-CoA reductase, nucleic acids encoding a lanosterol C14-demethylase, nucleic acids encoding a squalene epoxidase, nucleic acids encoding a squalene synthetase and nucleic acids encoding a sterol acyltransferase, which are functionally linked with one or more regulatory signals ensuring transcription and translation in organisms.
 44. A combination of nucleic acid constructs, which comprises at least one nucleic acid construct selected from the groups A to C A nucleic acid construct comprising nucleic acids encoding a Δ8-Δ7-isomerase, which are functionally linked to one or more regulatory signals ensuring transcription and translation in organisms, B nucleic acid construct comprising nucleic acids encoding a Δ5-desaturase, which are functionally linked to one or more regulatory signals ensuring transcription and translation in organisms and C nucleic acid construct comprising nucleic acids encoding a Δ24-reductase, which are functionally linked to one or more regulatory signals ensuring transcription and translation in organisms, and at least one nucleic acid construct selected from the groups D to H D nucleic acid construct comprising nucleic acids encoding an HMG-CoA reductase, which are functionally linked to one or more regulatory signals ensuring transcription and translation in organisms, E nucleic acid construct comprising nucleic acids encoding a lanosterol C14-demethylase, which are functionally linked to one or more regulatory signals ensuring transcription and translation in organisms, F nucleic acid construct comprising nucleic acids encoding a squalene epoxidase, which are functionally linked to one or more regulatory signals ensuring transcription and translation in organisms, G nucleic acid construct comprising nucleic acids encoding a squalene synthetase, which are functionally linked to one or more regulatory signals ensuring transcription and translation in organisms, H nucleic acid construct comprising nucleic acids encoding a sterol acyltransferase, which are functionally linked to one or more regulatory signals ensuring transcription and translation in organisms.
 45. The nucleic acid construct of claim 42, wherein the regulatory signals comprise one or more promoters and one or more terminators, which ensure transcription and translation in organisms.
 46. The nucleic acid construct of claim 42, wherein regulatory signals ensuring transcription and translation in yeasts are used.
 47. A genetically modified organism, wherein the genetic modification increases at least one of the activities selected from the group consisting of Δ8-Δ7-isomerase activity, Δ5-desaturase activity and Δ24-reductase activity, compared to a wild type.
 48. The genetically modified organism of claim 47, wherein the increase of at least one of the activities is caused by an increase in gene expression of at least one nucleic acid selected from the group consisting of nucleic acids encoding a Δ8-Δ7-isomerase, nucleic acids encoding a Δ5-desaturase and nucleic acids encoding a Δ24-reductase, compared to the wild type.
 49. The genetically modified organism of claim 48, which contains two or more nucleic acids encoding a Δ8-47-isomerase and/or two or more nucleic acids encoding a Δ5-desaturase and/or two or more nucleic acids encoding a Δ24-reductase.
 50. The genetically modified organism of claim 47, wherein the genetic modification additionally reduces at least one of the activities selected from the group consisting of C24-methyltransferase activity and Δ22-desaturase activity compared to a wild type.
 51. The genetically modified organism of claim 50, wherein the reduction in at least one of the activities is caused by a reduction in gene expression of at least one nucleic acid selected from the group consisting of nucleic acids encoding a C24-methyltransferase and nucleic acids encoding a Δ 22-desaturase, compared to the wild type.
 52. The genetically modified organism of claim 51, which has no functional C24-methyltransferase gene and/or Δ 22-desaturase gene.
 53. The genetically modified organism of claim 47, wherein the genetic modification additionally increases at least one of the activities selected from the group consisting of HMG-CoA-reductase activity, lanosterol C14-demethylase activity, squalene-epoxidase activity, squalene-synthetase activity and sterol-acyltransferase activity, compared to a wild type.
 54. The genetically modified organism of claim 53, wherein the increase in at least one of the activities is caused by an increase in gene expression of at least one nucleic acid selected from the group consisting of nucleic acids encoding an HMG-CoA-reductase activity, nucleic acids encoding a lanosterol C14-demethylase, nucleic acids encoding a squalene epoxidase, nucleic acids encoding a squalene synthetase and nucleic acids encoding a sterol acyltransferase, compared to the wild type.
 55. The genetically modified organism of claim 54, which contains two or more nucleic acids encoding an HMG-CoA reductase and/or two or more nucleic acids encoding a lanosterol C14-demethylase and/or two or more nucleic acids encoding a squalene epoxidase and/or two or more nucleic acids encoding a squalene synthetase and/or two or more nucleic acids encoding a sterol acyltransferase.
 56. The genetically modified organism of claim 47, which, compared to the wild type, has an increased content of 7-dehydrocholesterol and/or the biosynthetic intermediates and/or secondary products thereof.
 57. The genetically modified organism of claim 47, wherein the organism used is yeast.
 58. The use of a genetically modified organism claim 47 for preparing 7-dehydrocholesterol and/or the biosynthetic intermediates and/or secondary products thereof.
 59. The combination of nucleic acid constructs of claim 44, wherein the regulatory signals comprise one or more promoters and one or more terminators, which ensure transcription and translation in organisms.
 60. The combination of nucleic acid constructs of claim 44, wherein regulatory signals ensuring transcription and translation in yeasts are used. 